Initial data commit

2023-07-01 11:58:00 -04:00 · 2023-07-01 11:58:00 -04:00 · f23f22d71c
commit f23f22d71c
parent 72d218235f
199087 changed files with 3378941 additions and 0 deletions
--- a/Task/Merge-and-aggregate-datasets/00-META.yaml
+++ b/Task/Merge-and-aggregate-datasets/00-META.yaml
@ -0,0 +1,3 @@
+---
+from: http://rosettacode.org/wiki/Merge_and_aggregate_datasets
+note: Data Structures
--- a/Task/Merge-and-aggregate-datasets/00-TASK.txt
+++ b/Task/Merge-and-aggregate-datasets/00-TASK.txt
@ -0,0 +1,67 @@
+Merge and aggregate datasets
+
+
+;Task:
+Merge and aggregate two datasets as provided in &nbsp; '''.csv''' &nbsp; files into a new resulting dataset.
+
+Use the appropriate methods and data structures depending on the programming language. 
+
+Use the most common libraries only when built-in functionality is not sufficient.
+
+
+;Note:
+Either load the data from the &nbsp; '''.csv''' &nbsp; files or create the required data structures hard-coded.
+
+
+'''patients.csv''' &nbsp; file contents:
+<pre>
+PATIENT_ID,LASTNAME
+1001,Hopper
+4004,Wirth
+3003,Kemeny
+2002,Gosling
+5005,Kurtz
+</pre>
+
+
+'''visits.csv''' &nbsp; file contents:
+<pre>
+PATIENT_ID,VISIT_DATE,SCORE
+2002,2020-09-10,6.8
+1001,2020-09-17,5.5
+4004,2020-09-24,8.4
+2002,2020-10-08,
+1001,,6.6
+3003,2020-11-12,
+4004,2020-11-05,7.0
+1001,2020-11-19,5.3
+</pre>
+
+
+Create a resulting dataset in-memory or output it to screen or file, whichever is appropriate for the programming language at hand.
+
+Merge and group per patient id and last name, &nbsp; get the maximum visit date, &nbsp; and get the sum and average of the scores per patient to get the resulting dataset.
+
+
+Note that the visit date is purposefully provided as ISO format, &nbsp; so that it could also be processed as text and sorted alphabetically to determine the maximum date.
+<pre>
+| PATIENT_ID | LASTNAME | LAST_VISIT |  SCORE_SUM | SCORE_AVG |
+| 1001       |  Hopper  | 2020-11-19 |  17.4      | 5.80      |
+| 2002       |  Gosling | 2020-10-08 |   6.8      | 6.80      |
+| 3003       |  Kemeny  | 2020-11-12 |            |           |
+| 4004       |  Wirth   | 2020-11-05 |  15.4      | 7.70      |
+| 5005       |  Kurtz   |            |            |           |
+</pre>
+
+
+;Note:
+This task is aimed in particular at programming languages that are used in data science and data processing, such as F#, Python, R, SPSS, MATLAB etc.
+
+
+;Related tasks:
+* [[CSV data manipulation]]
+* [[CSV to HTML translation]]
+* [[Read entire file]]
+* [[Read a file line by line]]
+<br><br>
+
--- a/Task/Merge-and-aggregate-datasets/11l/merge-and-aggregate-datasets.11l
+++ b/Task/Merge-and-aggregate-datasets/11l/merge-and-aggregate-datasets.11l
@ -0,0 +1,55 @@
+V patients_csv =
+‘PATIENT_ID,LASTNAME
+1001,Hopper
+4004,Wirth
+3003,Kemeny
+2002,Gosling
+5005,Kurtz’
+
+V visits_csv =
+‘PATIENT_ID,VISIT_DATE,SCORE
+2002,2020-09-10,6.8
+1001,2020-09-17,5.5
+4004,2020-09-24,8.4
+2002,2020-10-08,
+1001,,6.6
+3003,2020-11-12,
+4004,2020-11-05,7.0
+1001,2020-11-19,5.3’
+
+F csv2list(s)
+   [[String]] rows
+   L(row) s.split("\n")
+      rows [+]= row.split(‘,’)
+   R rows
+
+V patients = csv2list(patients_csv)
+V visits = csv2list(visits_csv)
+
+V result = copy(patients)
+result.sort_range(1..)
+result[0].append(‘LAST_VISIT’)
+V last = Dict(visits[1..], p_vis -> (p_vis[0], p_vis[1]))
+L(record) 1 .< result.len
+   result[record].append(last.get(result[record][0], ‘’))
+result[0] [+]= [‘SCORE_SUM’, ‘SCORE_AVG’]
+
+V n = Dict(patients[1..], p -> (p[0], 0))
+V tot = Dict(patients[1..], p -> (p[0], 0.0))
+
+L(record) visits[1..]
+   V p = record[0]
+   V score = record[2]
+   I !score.empty
+      n[p]++
+      tot[p] += Float(score)
+
+L(record) 1 .< result.len
+   V p = result[record][0]
+   I n[p] != 0
+      result[record] [+]= [‘#3.1’.format(tot[p]), ‘#2.2’.format(tot[p] / n[p])]
+   E
+      result[record] [+]= [‘’, ‘’]
+
+L(record) result
+   print(‘| ’record.map(r -> r.center(10)).join(‘ | ’)‘ |’)
--- a/Task/Merge-and-aggregate-datasets/AWK/merge-and-aggregate-datasets.awk
+++ b/Task/Merge-and-aggregate-datasets/AWK/merge-and-aggregate-datasets.awk
@ -0,0 +1,38 @@
+# syntax: GAWK -f MERGE_AND_AGGREGATE_DATASETS.AWK RC-PATIENTS.CSV RC-VISITS.CSV
+# files may appear in any order
+#
+# sorting:
+#   PROCINFO["sorted_in"] is used by GAWK
+#   SORTTYPE is used by Thompson Automation's TAWK
+#
+{ # printf("%s %s\n",FILENAME,$0) # print input
+    split($0,arr,",")
+    if (FNR == 1) {
+      file = (arr[2] == "LASTNAME") ? "patients" : "visits"
+      next
+    }
+    patient_id_arr[key] = key = arr[1]
+    if (file == "patients") {
+      lastname_arr[key] = arr[2]
+    }
+    else if (file == "visits") {
+      if (arr[2] > visit_date_arr[key]) {
+        visit_date_arr[key] = arr[2]
+      }
+      if (arr[3] != "") {
+        score_arr[key] += arr[3]
+        score_count_arr[key]++
+      }
+    }
+}
+END {
+    print("")
+    PROCINFO["sorted_in"] = "@ind_str_asc" ; SORTTYPE = 1
+    fmt = "%-10s %-10s %-10s %9s %9s %6s\n"
+    printf(fmt,"patient_id","lastname","last_visit","score_sum","score_avg","scores")
+    for (i in patient_id_arr) {
+      avg = (score_count_arr[i] > 0) ? score_arr[i] / score_count_arr[i] : ""
+      printf(fmt,patient_id_arr[i],lastname_arr[i],visit_date_arr[i],score_arr[i],avg,score_count_arr[i]+0)
+    }
+    exit(0)
+}
--- a/Task/Merge-and-aggregate-datasets/AutoHotkey/merge-and-aggregate-datasets-1.ahk
+++ b/Task/Merge-and-aggregate-datasets/AutoHotkey/merge-and-aggregate-datasets-1.ahk
@ -0,0 +1,24 @@
+Merge_and_aggregate(patients, visits){
+    ID := [], LAST_VISIT := [], SCORE_SUM := [], VISIT := []
+    for i, line in StrSplit(patients, "`n", "`r"){
+        if (i=1)
+            continue
+        x := StrSplit(line, ",")
+        ID[x.1] := x.2
+    }
+
+    for i, line in StrSplit(visits, "`n", "`r"){
+        if (i=1)
+            continue
+        x := StrSplit(line, ",")
+        LAST_VISIT[x.1] := x.2 > LAST_VISIT[x.1] ? x.2 : LAST_VISIT[x.1]
+        SCORE_SUM[x.1] := (SCORE_SUM[x.1] ? SCORE_SUM[x.1] : 0) + (x.3 ? x.3 : 0)
+        if x.3
+            VISIT[x.1] := (VISIT[x.1] ? VISIT[x.1] : 0) + 1
+    }
+
+    output := "PATIENT_ID`tLASTNAME`tLAST_VISIT`tSCORE_SUM`tSCORE_AVG`n"
+    for id, name in ID
+        output .= ID "`t" name "`t" LAST_VISIT[id] "`t" SCORE_SUM[id] "`t" SCORE_SUM[id]/VISIT[id] "`n"
+    return output
+}
--- a/Task/Merge-and-aggregate-datasets/AutoHotkey/merge-and-aggregate-datasets-2.ahk
+++ b/Task/Merge-and-aggregate-datasets/AutoHotkey/merge-and-aggregate-datasets-2.ahk
@ -0,0 +1,25 @@
+patients =
+(
+PATIENT_ID,LASTNAME
+1001,Hopper
+4004,Wirth
+3003,Kemeny
+2002,Gosling
+5005,Kurtz
+)
+
+visits =
+(
+PATIENT_ID,VISIT_DATE,SCORE
+2002,2020-09-10,6.8
+1001,2020-09-17,5.5
+4004,2020-09-24,8.4
+2002,2020-10-08,
+1001,,6.6
+3003,2020-11-12,
+4004,2020-11-05,7.0
+1001,2020-11-19,5.3
+)
+
+MsgBox % Merge_and_aggregate(patients, visits)
+return
--- a/Task/Merge-and-aggregate-datasets/C++/merge-and-aggregate-datasets.cpp
+++ b/Task/Merge-and-aggregate-datasets/C++/merge-and-aggregate-datasets.cpp
@ -0,0 +1,77 @@
+#include <iostream>
+#include <optional>
+#include <ranges>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+struct Patient
+{
+    string ID;
+    string LastName;
+};
+
+struct Visit
+{
+    string PatientID;
+    string Date;
+    optional<float> Score;
+};
+
+int main(void)
+{
+    auto patients = vector<Patient> {
+        {"1001", "Hopper"},
+        {"4004", "Wirth"},
+        {"3003", "Kemeny"},
+        {"2002", "Gosling"},
+        {"5005", "Kurtz"}};
+
+    auto visits = vector<Visit> {
+        {"2002", "2020-09-10", 6.8},
+        {"1001", "2020-09-17", 5.5},
+        {"4004", "2020-09-24", 8.4},
+        {"2002", "2020-10-08", },
+        {"1001", ""          , 6.6},
+        {"3003", "2020-11-12", },
+        {"4004", "2020-11-05", 7.0},
+        {"1001", "2020-11-19", 5.3}};
+
+    // sort the patients by ID
+    sort(patients.begin(), patients.end(),
+         [](const auto& a, const auto&b){ return a.ID < b.ID;});
+
+    cout << "| PATIENT_ID | LASTNAME | LAST_VISIT | SCORE_SUM | SCORE_AVG |\n";
+    for(const auto& patient : patients)
+    {
+        // loop over all of the patients and determine the fields
+        string lastVisit;
+        float sum = 0;
+        int numScores = 0;
+
+        // use C++20 ranges to filter the visits by patients
+        auto patientFilter = [&patient](const Visit &v){return v.PatientID == patient.ID;};
+        for(const auto& visit : visits | views::filter( patientFilter ))
+        {
+            if(visit.Score)
+            {
+                sum += *visit.Score;
+                numScores++;
+            }
+            lastVisit = max(lastVisit, visit.Date);
+        }
+
+        // format the output
+        cout << "|       " << patient.ID << " | ";
+        cout.width(8); cout << patient.LastName << " | ";
+        cout.width(10); cout << lastVisit << " | ";
+        if(numScores > 0)
+        {
+            cout.width(9); cout << sum << " | ";
+            cout.width(9); cout << (sum / float(numScores));
+        }
+        else cout << "          |          ";
+        cout << " |\n";
+    }
+}
--- a/Task/Merge-and-aggregate-datasets/C-sharp/merge-and-aggregate-datasets.cs
+++ b/Task/Merge-and-aggregate-datasets/C-sharp/merge-and-aggregate-datasets.cs
@ -0,0 +1,73 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Runtime.Serialization;
+
+public static class MergeAndAggregateDatasets
+{
+    public static void Main()
+    {
+        string patientsCsv = @"
+PATIENT_ID,LASTNAME
+1001,Hopper
+4004,Wirth
+3003,Kemeny
+2002,Gosling
+5005,Kurtz";
+
+        string visitsCsv = @"
+PATIENT_ID,VISIT_DATE,SCORE
+2002,2020-09-10,6.8
+1001,2020-09-17,5.5
+4004,2020-09-24,8.4
+2002,2020-10-08,
+1001,,6.6
+3003,2020-11-12,
+4004,2020-11-05,7.0
+1001,2020-11-19,5.3";
+
+        string format = "yyyy-MM-dd";
+        var formatProvider = new DateTimeFormat(format).FormatProvider;
+
+        var patients = ParseCsv(
+            patientsCsv.Split(Environment.NewLine, StringSplitOptions.RemoveEmptyEntries),
+            line => (PatientId: int.Parse(line[0]), LastName: line[1]));
+
+        var visits = ParseCsv(
+            visitsCsv.Split(Environment.NewLine, StringSplitOptions.RemoveEmptyEntries),
+            line => (
+                PatientId: int.Parse(line[0]),
+                VisitDate: DateTime.TryParse(line[1], formatProvider, DateTimeStyles.None, out var date) ? date : default(DateTime?),
+                Score: double.TryParse(line[2], out double score) ? score : default(double?)
+            )
+        );
+
+        var results =
+            patients.GroupJoin(visits,
+                p => p.PatientId,
+                v => v.PatientId,
+                (p, vs) => (
+                    p.PatientId,
+                    p.LastName,
+                    LastVisit: vs.Max(v => v.VisitDate),
+                    ScoreSum: vs.Sum(v => v.Score),
+                    ScoreAvg: vs.Average(v => v.Score)
+                )
+            ).OrderBy(r => r.PatientId);
+
+        Console.WriteLine("| PATIENT_ID | LASTNAME | LAST_VISIT | SCORE_SUM | SCORE_AVG |");
+        foreach (var r in results) {
+            Console.WriteLine($"| {r.PatientId,-10} | {r.LastName,-8} | {r.LastVisit?.ToString(format) ?? "",-10} | {r.ScoreSum,9} | {r.ScoreAvg,9} |");
+        }
+    }
+
+    private static IEnumerable<T> ParseCsv<T>(string[] contents, Func<string[], T> constructor)
+    {
+        for (int i = 1; i < contents.Length; i++) {
+            var line = contents[i].Split(',');
+            yield return constructor(line);
+        }
+    }
+
+}
--- a/Task/Merge-and-aggregate-datasets/Datalog/merge-and-aggregate-datasets-1.datalog
+++ b/Task/Merge-and-aggregate-datasets/Datalog/merge-and-aggregate-datasets-1.datalog
@ -0,0 +1,10 @@
+// datetime.cpp
+#include <ctime>
+#include <cstdint>
+extern "C" {
+  int64_t from date(const char* string) {
+    struct tm tmInfo = {0};
+    strptime(string, "%Y-%m-%d", &tmInfo);
+    return mktime(&tmInfo); // localtime
+  }
+}
--- a/Task/Merge-and-aggregate-datasets/Datalog/merge-and-aggregate-datasets-2.datalog
+++ b/Task/Merge-and-aggregate-datasets/Datalog/merge-and-aggregate-datasets-2.datalog
@ -0,0 +1,36 @@
+/* rosetta.dl */
+#define NaN to_float("NaN")
+.functor from_date(date:symbol) : number
+.decl Patient(id:number, lastname:symbol)
+.decl Visit(id:number, date:symbol, score:float)
+.decl SummaryDates(id:number, lastname:symbol, last_date:symbol)
+.decl SummaryScores(id:number, lastname:symbol, score_sum:float, score_mean:float)
+.decl MissingDates(x:number)
+
+Patient(1001,"Hopper").
+Patient(4004,"Wirth").
+Patient(3003,"Kemeny").
+Patient(2002,"Gosling").
+Patient(5005,"Kurtz").
+
+Visit(2002,"2020-09-10",6.8).
+Visit(1001,"2020-09-17",5.5).
+Visit(4004,"2020-09-24",8.4).
+Visit(2002,"2020-10-08",NaN).
+Visit(1001,"",6.6).
+Visit(3003,"2020-11-12",NaN).
+Visit(4004,"2020-11-05",7.0).
+Visit(1001,"2020-11-19",5.3).
+
+MissingDates(@from_date("")) :- true.
+
+SummaryDates(id, lastname, last_date) :-
+     Patient(id,lastname),
+     last_timestamp = max ts: {Visit(id, date, _), ts = @from_date(date), !MissingDates(ts)},
+     Visit(id, last_date, _), last_timestamp = @from_date(last_date).
+SummaryScores(id, lastname, score_sum, score_mean) :-
+     Patient(id,lastname),
+     score_sum = sum score: {Visit(id, _, score), score != NaN},
+     score_mean = mean score: {Visit(id, _, score), score != NaN}.
+.output SummaryDates
+.output SummaryScores
--- a/Task/Merge-and-aggregate-datasets/Datalog/merge-and-aggregate-datasets-3.datalog
+++ b/Task/Merge-and-aggregate-datasets/Datalog/merge-and-aggregate-datasets-3.datalog
@ -0,0 +1,2 @@
+g++ -shared -fPIC datetime.cpp -o libfunctors.so
+souffle -D- rosetta.dl
--- a/Task/Merge-and-aggregate-datasets/F-Sharp/merge-and-aggregate-datasets.fs
+++ b/Task/Merge-and-aggregate-datasets/F-Sharp/merge-and-aggregate-datasets.fs
@ -0,0 +1,9 @@
+// Merge and aggregate datasets. Nigel Galloway: January 6th., 2021
+let rFile(fName)=seq{use n=System.IO.File.OpenText(fName)
+                     n.ReadLine() |> ignore
+                     while not n.EndOfStream do yield n.ReadLine().Split [|','|]}
+let N=rFile("file1.txt") |> Seq.sort
+let G=rFile("file2.txt") |> Seq.groupBy(fun n->n.[0]) |> Map.ofSeq
+let fN n i g e l=printfn "| %-10s | %-8s | %10s |  %-9s | %-9s |" n i g e l
+let fG n g=let z=G.[n]|>Seq.sumBy(fun n->try float n.[2] with :? System.FormatException->0.0)
+           fN n g (G.[n]|>Seq.sort|>Seq.last).[1] (if z=0.0 then "" else string z) (if z=0.0 then "" else string(z/(float(Seq.length G.[n]))))
--- a/Task/Merge-and-aggregate-datasets/Go/merge-and-aggregate-datasets.go
+++ b/Task/Merge-and-aggregate-datasets/Go/merge-and-aggregate-datasets.go
@ -0,0 +1,138 @@
+package main
+
+import (
+    "fmt"
+    "math"
+    "sort"
+)
+
+type Patient struct {
+    id       int
+    lastName string
+}
+
+// maps an id to a lastname
+var patientDir = make(map[int]string)
+
+// maintains a sorted list of ids
+var patientIds []int
+
+func patientNew(id int, lastName string) Patient {
+    patientDir[id] = lastName
+    patientIds = append(patientIds, id)
+    sort.Ints(patientIds)
+    return Patient{id, lastName}
+}
+
+type DS struct {
+    dates  []string
+    scores []float64
+}
+
+type Visit struct {
+    id    int
+    date  string
+    score float64
+}
+
+// maps an id to lists of dates and scores
+var visitDir = make(map[int]DS)
+
+func visitNew(id int, date string, score float64) Visit {
+    if date == "" {
+        date = "0000-00-00"
+    }
+    v, ok := visitDir[id]
+    if ok {
+        v.dates = append(v.dates, date)
+        v.scores = append(v.scores, score)
+        visitDir[id] = DS{v.dates, v.scores}
+    } else {
+        visitDir[id] = DS{[]string{date}, []float64{score}}
+    }
+    return Visit{id, date, score}
+}
+
+type Merge struct{ id int }
+
+func (m Merge) lastName() string  { return patientDir[m.id] }
+func (m Merge) dates() []string   { return visitDir[m.id].dates }
+func (m Merge) scores() []float64 { return visitDir[m.id].scores }
+
+func (m Merge) lastVisit() string {
+    dates := m.dates()
+    dates2 := make([]string, len(dates))
+    copy(dates2, dates)
+    sort.Strings(dates2)
+    return dates2[len(dates2)-1]
+}
+
+func (m Merge) scoreSum() float64 {
+    sum := 0.0
+    for _, score := range m.scores() {
+        if score != -1 {
+            sum += score
+        }
+    }
+    return sum
+}
+
+func (m Merge) scoreAvg() float64 {
+    count := 0
+    for _, score := range m.scores() {
+        if score != -1 {
+            count++
+        }
+    }
+    return m.scoreSum() / float64(count)
+}
+
+func mergePrint(merges []Merge) {
+    fmt.Println("| PATIENT_ID | LASTNAME | LAST_VISIT | SCORE_SUM | SCORE_AVG |")
+    f := "| %d       | %-7s  | %s | %4s      | %4s      |\n"
+    for _, m := range merges {
+        _, ok := visitDir[m.id]
+        if ok {
+            lv := m.lastVisit()
+            if lv == "0000-00-00" {
+                lv = "          "
+            }
+            scoreSum := m.scoreSum()
+            ss := fmt.Sprintf("%4.1f", scoreSum)
+            if scoreSum == 0 {
+                ss = "    "
+            }
+            scoreAvg := m.scoreAvg()
+            sa := "    "
+            if !math.IsNaN(scoreAvg) {
+                sa = fmt.Sprintf("%4.2f", scoreAvg)
+            }
+            fmt.Printf(f, m.id, m.lastName(), lv, ss, sa)
+        } else {
+            fmt.Printf(f, m.id, m.lastName(), "          ", "    ", "    ")
+        }
+    }
+}
+
+func main() {
+    patientNew(1001, "Hopper")
+    patientNew(4004, "Wirth")
+    patientNew(3003, "Kemeny")
+    patientNew(2002, "Gosling")
+    patientNew(5005, "Kurtz")
+
+    visitNew(2002, "2020-09-10", 6.8)
+    visitNew(1001, "2020-09-17", 5.5)
+    visitNew(4004, "2020-09-24", 8.4)
+    visitNew(2002, "2020-10-08", -1) // -1 signifies no score
+    visitNew(1001, "", 6.6)          // "" signifies no date
+    visitNew(3003, "2020-11-12", -1)
+    visitNew(4004, "2020-11-05", 7.0)
+    visitNew(1001, "2020-11-19", 5.3)
+
+    merges := make([]Merge, len(patientIds))
+    for i, id := range patientIds {
+        merges[i] = Merge{id}
+    }
+    mergePrint(merges)
+}
--- a/Task/Merge-and-aggregate-datasets/Haskell/merge-and-aggregate-datasets-1.hs
+++ b/Task/Merge-and-aggregate-datasets/Haskell/merge-and-aggregate-datasets-1.hs
@ -0,0 +1,66 @@
+import Data.List
+import Data.Maybe
+import System.IO (readFile)
+import Text.Read (readMaybe)
+import Control.Applicative ((<|>))
+
+------------------------------------------------------------
+
+newtype DB = DB { entries :: [Patient] }
+  deriving Show
+
+instance Semigroup DB where
+  DB a <> DB b = normalize $ a <> b
+
+instance Monoid DB where
+  mempty = DB []
+
+normalize :: [Patient] -> DB
+normalize = DB
+            . map mconcat
+            . groupBy (\x y -> pid x == pid y)
+            . sortOn pid
+
+------------------------------------------------------------
+
+data Patient = Patient { pid :: String
+                       , name :: Maybe String
+                       , visits :: [String]
+                       , scores :: [Float] }
+  deriving Show
+
+instance Semigroup Patient where
+  Patient p1 n1 v1 s1 <> Patient p2 n2 v2 s2 =
+    Patient (fromJust $ Just p1 <|> Just p2)
+            (n1 <|> n2)
+            (v1 <|> v2)
+            (s1 <|> s2)
+
+instance Monoid Patient where
+  mempty = Patient mempty mempty mempty mempty
+
+------------------------------------------------------------
+
+readDB :: String  -> DB
+readDB = normalize
+         . mapMaybe readPatient
+         . readCSV
+
+readPatient r = do
+  i <- lookup "PATIENT_ID" r
+  let n = lookup "LASTNAME" r
+  let d = lookup "VISIT_DATE" r >>= readDate
+  let s = lookup "SCORE" r >>= readMaybe
+  return $ Patient i n (maybeToList d) (maybeToList s)
+  where
+    readDate [] = Nothing
+    readDate d = Just d
+
+readCSV :: String -> [(String, String)]
+readCSV txt = zip header <$> body
+  where
+    header:body = splitBy ',' <$> lines txt
+    splitBy ch = unfoldr go
+      where
+        go [] = Nothing
+        go s  = Just $ drop 1 <$> span (/= ch) s
--- a/Task/Merge-and-aggregate-datasets/Haskell/merge-and-aggregate-datasets-2.hs
+++ b/Task/Merge-and-aggregate-datasets/Haskell/merge-and-aggregate-datasets-2.hs
@ -0,0 +1,22 @@
+tabulateDB (DB ps) header cols = intercalate "|" <$> body
+  where
+    body = transpose $ zipWith pad width table
+    table = transpose $ header : map showPatient ps
+    showPatient p = sequence cols p
+    width = maximum . map length <$> table
+    pad n col = (' ' :) . take (n+1) . (++ repeat ' ') <$> col
+
+main = do
+  a <- readDB <$> readFile "patients.csv"
+  b <- readDB <$> readFile "visits.csv"
+  mapM_ putStrLn $ tabulateDB (a <> b) header fields
+  where
+    header = [ "PATIENT_ID", "LASTNAME", "VISIT_DATE"
+             , "SCORES SUM","SCORES AVG"]
+    fields = [ pid
+             , fromMaybe [] . name
+             , \p -> case visits p of {[] -> []; l -> last l}
+             , \p -> case scores p of {[] -> []; s -> show (sum s)}
+             , \p -> case scores p of {[] -> []; s -> show (mean s)} ]
+
+    mean lst = sum lst / genericLength lst
--- a/Task/Merge-and-aggregate-datasets/J/merge-and-aggregate-datasets-1.j
+++ b/Task/Merge-and-aggregate-datasets/J/merge-and-aggregate-datasets-1.j
@ -0,0 +1,34 @@
+NB. setup:
+require'jd pacman'
+load JDP,'tools/csv_load.ijs'
+F=: jpath '~temp/rosettacode/example/CSV'
+jdcreatefolder_jd_ CSVFOLDER=: F
+
+assert 0<{{)n
+PATIENTID,LASTNAME
+1001,Hopper
+4004,Wirth
+3003,Kemeny
+2002,Gosling
+5005,Kurtz
+}} fwrite F,'patients.csv'
+
+assert 0<{{)n
+PATIENTID,VISIT_DATE,SCORE
+2002,2020-09-10,6.8
+1001,2020-09-17,5.5
+4004,2020-09-24,8.4
+2002,2020-10-08,
+1001,,6.6
+3003,2020-11-12,
+4004,2020-11-05,7.0
+1001,2020-11-19,5.3
+}} fwrite F,'visits.csv'
+
+csvprepare 'patients';F,'patients.csv'
+csvprepare 'visits';F,'visits.csv'
+
+csvload 'patients';1
+csvload 'visits';1
+
+jd'ref patients PATIENTID  visits PATIENTID'
--- a/Task/Merge-and-aggregate-datasets/J/merge-and-aggregate-datasets-2.j
+++ b/Task/Merge-and-aggregate-datasets/J/merge-and-aggregate-datasets-2.j
@ -0,0 +1,15 @@
+require'jd'
+
+echo jd {{)n
+  reads
+        PATIENT_ID: first p.PATIENTID,
+        LASTNAME:   first p.LASTNAME,
+        LAST_VISIT: max v.VISIT_DATE,
+        SCORE_SUM:  sum v.SCORE,
+        SCORE_AVG:  avg v.SCORE
+    by
+      p.PATIENTID
+    from
+      p:patients,
+      v:p.visits
+}} -.LF
--- a/Task/Merge-and-aggregate-datasets/J/merge-and-aggregate-datasets-3.j
+++ b/Task/Merge-and-aggregate-datasets/J/merge-and-aggregate-datasets-3.j
@ -0,0 +1,37 @@
+require'csv'
+patients=: fixcsv {{)n
+PATIENTID,LASTNAME
+1001,Hopper
+4004,Wirth
+3003,Kemeny
+2002,Gosling
+5005,Kurtz
+}}
+
+visits=: fixcsv {{)n
+PATIENTID,VISIT_DATE,SCORE
+2002,2020-09-10,6.8
+1001,2020-09-17,5.5
+4004,2020-09-24,8.4
+2002,2020-10-08,
+1001,,6.6
+3003,2020-11-12,
+4004,2020-11-05,7.0
+1001,2020-11-19,5.3
+}}
+
+task=: {{
+  P=. <@:>"1|:/:~}.patients
+  V=. <@:>"1|:/:~}.visits
+  id=. 0 {:: P
+  nm=. 1 {:: P
+  sel1=. (0 {:: P) e. 0 {:: V
+  sel2=. (~.0 {:: V) e. 0 {:: P NB. unnecessary for this example
+  exp=. sel1 #inv sel2 # ]
+  agg=. /.(&.:".)
+  vdt=. exp     (0 {:: V) {:/.         1 {:: V
+  sum=. exp ":,.(0 {:: V) +//.     0". 2 {:: V
+  avg=. exp ":,.(0 {:: V) (+/%#)/. 0". 2 {:: V
+  labels=. ;:'PATIENT_ID LASTNAME LAST_VISIT SCORE_SUM SCORE_AVG'
+  labels,:id;nm;vdt;sum;avg
+}}
--- a/Task/Merge-and-aggregate-datasets/J/merge-and-aggregate-datasets-4.j
+++ b/Task/Merge-and-aggregate-datasets/J/merge-and-aggregate-datasets-4.j
@ -0,0 +1,10 @@
+   task''
+┌──────────┬────────┬──────────┬─────────┬─────────┐
+│PATIENT_ID│LASTNAME│LAST_VISIT│SCORE_SUM│SCORE_AVG│
+├──────────┼────────┼──────────┼─────────┼─────────┤
+│1001      │Hopper  │2020-11-19│17.4     │5.8      │
+│2002      │Gosling │2020-10-08│ 6.8     │3.4      │
+│3003      │Kemeny  │2020-11-12│   0     │  0      │
+│4004      │Wirth   │2020-11-05│15.4     │7.7      │
+│5005      │Kurtz   │          │         │         │
+└──────────┴────────┴──────────┴─────────┴─────────┘
--- a/Task/Merge-and-aggregate-datasets/J/merge-and-aggregate-datasets-5.j
+++ b/Task/Merge-and-aggregate-datasets/J/merge-and-aggregate-datasets-5.j
@ -0,0 +1,17 @@
+task=: {{
+  P=. <@:>"1|:/:~}.patients
+  V=. <@:>"1|:/:~}.visits
+  id=. 0 {:: P
+  nm=. 1 {:: P
+  sel1=. (0 {:: P) e. 0 {:: V
+  sel2=. (~.0 {:: V) e. 0 {:: P NB. unnecessary for this example
+  exp=. sel1 #inv sel2 # ]
+  agg=. /.(&.:".)
+  vdt=. exp     (0 {:: V) {:/.          1 {:: V
+  sel3=. (0 {:: V) +.//. 2 *@#@{::"1 }.visits
+  exp2=: [:exp sel3 #inv sel3 #]
+  sum=. exp2 ":,.(0 {:: V) +//.     0". 2 {:: V
+  avg=. exp2 ":,.(0 {:: V) (+/%#)/. 0". 2 {:: V
+  labels=. ;:'PATIENT_ID LASTNAME LAST_VISIT SCORE_SUM SCORE_AVG'
+  labels,:id;nm;vdt;sum;avg
+}}
--- a/Task/Merge-and-aggregate-datasets/J/merge-and-aggregate-datasets-6.j
+++ b/Task/Merge-and-aggregate-datasets/J/merge-and-aggregate-datasets-6.j
@ -0,0 +1,10 @@
+   task''
+┌──────────┬────────┬──────────┬─────────┬─────────┐
+│PATIENT_ID│LASTNAME│LAST_VISIT│SCORE_SUM│SCORE_AVG│
+├──────────┼────────┼──────────┼─────────┼─────────┤
+│1001      │Hopper  │2020-11-19│17.4     │5.8      │
+│2002      │Gosling │2020-10-08│ 6.8     │3.4      │
+│3003      │Kemeny  │2020-11-12│         │         │
+│4004      │Wirth   │2020-11-05│15.4     │7.7      │
+│5005      │Kurtz   │          │         │         │
+└──────────┴────────┴──────────┴─────────┴─────────┘
--- a/Task/Merge-and-aggregate-datasets/Java/merge-and-aggregate-datasets.java
+++ b/Task/Merge-and-aggregate-datasets/Java/merge-and-aggregate-datasets.java
@ -0,0 +1,47 @@
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.DoubleSummaryStatistics;
+import java.util.List;
+
+public final class MergeAndAggregateDatasets {
+
+	public static void main(String[] args) {
+		List<Patient> patients = Arrays.asList(
+			new Patient("1001", "Hopper"),
+			new Patient("4004", "Wirth"),
+			new Patient("3003", "Kemeny"),
+			new Patient("2002", "Gosling"),
+			new Patient("5005", "Kurtz") );
+
+		List<Visit> visits = Arrays.asList(				
+		    new Visit("2002", "2020-09-10", 6.8),
+		    new Visit("1001", "2020-09-17", 5.5),
+		    new Visit("4004", "2020-09-24", 8.4),
+		    new Visit("2002", "2020-10-08", null),
+		    new Visit("1001", ""          , 6.6),
+		    new Visit("3003", "2020-11-12", null),
+		    new Visit("4004", "2020-11-05", 7.0),
+		    new Visit("1001", "2020-11-19", 5.3) );
+		
+		Collections.sort(patients, Comparator.comparing(Patient::patientID));		
+		System.out.println("| PATIENT_ID | LASTNAME | LAST_VISIT | SCORE_SUM | SCORE_AVG |");		
+	    for ( Patient patient : patients ) {	    	
+	    	List<Visit> patientVisits = visits.stream().filter( v -> v.visitID == patient.patientID() ).toList();
+	    	String lastVisit = patientVisits.stream()
+	    		.map( v -> v.visitDate ).max(Comparator.naturalOrder()).orElseGet( () -> "   None   " );	    	
+	    	DoubleSummaryStatistics statistics = patientVisits.stream()
+	    		.filter( v -> v.score != null ).mapToDouble(Visit::score).summaryStatistics();	    		    	
+	    	double scoreSum = statistics.getSum();
+	    	double scoreAverage = statistics.getAverage();	    	
+	    	String patientDetails = String.format("%12s%11s%13s%12.2f%12.2f",
+	    		patient.patientID, patient.lastName, lastVisit, scoreSum, scoreAverage);	    	
+	    	System.out.println(patientDetails);
+	    }
+
+        private static record Patient(String patientID, String lastName) {};
+	    private static record Visit(String visitID, String visitDate, Double score) {};
+
+	}
+
+}
--- a/Task/Merge-and-aggregate-datasets/Jq/merge-and-aggregate-datasets-1.jq
+++ b/Task/Merge-and-aggregate-datasets/Jq/merge-and-aggregate-datasets-1.jq
@ -0,0 +1,16 @@
+# objectify/1 takes an array of atomic values as inputs, and packages
+# these into an object with keys specified by the "headers" array and
+# values obtained by trimming string values, replacing empty strings
+# by null, and converting strings to numbers if possible.
+def objectify(headers):
+  def tonumberq: tonumber? // .;
+  def trimq: if type == "string" then sub("^ +";"") | sub(" +$";"") else . end;
+  def tonullq: if . == "" then null else . end;
+  . as $in
+  | reduce range(0; headers|length) as $i
+      ({}; .[headers[$i]] = ($in[$i] | trimq | tonumberq | tonullq) );
+
+def csv2jsonHelper:
+  .[0] as $headers
+  | reduce (.[1:][] | select(length > 0) ) as $row
+      ([]; . + [ $row|objectify($headers) ]);
--- a/Task/Merge-and-aggregate-datasets/Jq/merge-and-aggregate-datasets-2.jq
+++ b/Task/Merge-and-aggregate-datasets/Jq/merge-and-aggregate-datasets-2.jq
@ -0,0 +1,9 @@
+# output {LAST_VISIT}
+def LAST_VISIT($patient_id):
+  {LAST_VISIT: (map(select( .PATIENT_ID == $patient_id).VISIT_DATE) | max)};
+
+# output {SCORE_SUM, SCORE_AVG}
+def SCORE_SUMMARY($patient_id):
+  map(select( .PATIENT_ID == $patient_id).SCORE)
+  | {SCORE_SUM: add, count: length}
+  | {SCORE_SUM, SCORE_AVG: (if .SCORE_SUM and .count > 0 then .SCORE_SUM/.count else null end)};
--- a/Task/Merge-and-aggregate-datasets/Jq/merge-and-aggregate-datasets-3.jq
+++ b/Task/Merge-and-aggregate-datasets/Jq/merge-and-aggregate-datasets-3.jq
@ -0,0 +1,10 @@
+# Read the two tables:
+INDEX($patients | [splits("\n")] | map(split(",")) | csv2jsonHelper[]; .PATIENT_ID) as $patients
+| ($visits | [splits("\n")] | map(split(",")) | csv2jsonHelper) as $visits
+# Construct the new table:
+| $visits
+| map(.PATIENT_ID as $PATIENT_ID
+      | {$PATIENT_ID}  +
+        ($visits | {LASTNAME: $patients[$PATIENT_ID|tostring]} + LAST_VISIT($PATIENT_ID) + SCORE_SUMMARY($PATIENT_ID)))
+# ... but display it as a sequence of JSON objects
+| .[]
--- a/Task/Merge-and-aggregate-datasets/Julia/merge-and-aggregate-datasets.julia
+++ b/Task/Merge-and-aggregate-datasets/Julia/merge-and-aggregate-datasets.julia
@ -0,0 +1,39 @@
+using CSV, DataFrames, Statistics
+
+# load data from csv files
+#df_patients = CSV.read("patients.csv", DataFrame)
+#df_visits = CSV.read("visits.csv", DataFrame)
+
+# create DataFrames from text that is hard coded, so use IOBuffer(String) as input
+str_patients = IOBuffer("""PATIENT_ID,LASTNAME
+1001,Hopper
+4004,Wirth
+3003,Kemeny
+2002,Gosling
+5005,Kurtz
+""")
+df_patients = CSV.read(str_patients, DataFrame)
+str_visits = IOBuffer("""PATIENT_ID,VISIT_DATE,SCORE
+2002,2020-09-10,6.8
+1001,2020-09-17,5.5
+4004,2020-09-24,8.4
+2002,2020-10-08,
+1001,,6.6
+3003,2020-11-12,
+4004,2020-11-05,7.0
+1001,2020-11-19,5.3
+""")
+df_visits = CSV.read(str_visits, DataFrame)
+
+# merge on PATIENT_ID, using an :outer join or we lose Kurtz, who has no data, sort by ID
+df_merge = sort(join(df_patients, df_visits, on="PATIENT_ID", kind=:outer), (:PATIENT_ID,))
+
+fnonmissing(a, f) = isempty(a) ? [] : isempty(skipmissing(a)) ? a[1] : f(skipmissing(a))
+
+# group by patient id / last name and then aggregate to get latest visit and mean score
+df_result = by(df_merge, [:PATIENT_ID, :LASTNAME]) do df
+    DataFrame(LATEST_VISIT = fnonmissing(df[:VISIT_DATE], maximum),
+              SUM_SCORE = fnonmissing(df[:SCORE], sum),
+              MEAN_SCORE = fnonmissing(df[:SCORE], mean))
+end
+println(df_result)
--- a/Task/Merge-and-aggregate-datasets/Mathematica/merge-and-aggregate-datasets.math
+++ b/Task/Merge-and-aggregate-datasets/Mathematica/merge-and-aggregate-datasets.math
@ -0,0 +1,25 @@
+a = ImportString["PATIENT_ID,LASTNAME
+1001,Hopper
+4004,Wirth
+3003,Kemeny
+2002,Gosling
+5005,Kurtz", "CSV"];
+b = ImportString["PATIENT_ID,VISIT_DATE,SCORE
+2002,2020-09-10,6.8
+1001,2020-09-17,5.5
+4004,2020-09-24,8.4
+2002,2020-10-08,
+1001,,6.6
+3003,2020-11-12,
+4004,2020-11-05,7.0
+1001,2020-11-19,5.3", "CSV"];
+a = <|a[[1, 1]] -> #1, a[[1, 2]] -> #2|> & @@@ Rest[a];
+b = <|b[[1, 1]] -> #1, b[[1, 2]] -> If[#2 != "", DateObject[#2], Missing[]], b[[1, 3]] -> If[#3 =!= "", #3, Missing[]]|> & @@@ Rest[b];
+j = JoinAcross[a, b, Key["PATIENT_ID"], "Outer"];
+gr = GroupBy[j, #["PATIENT_ID"] &];
+<|"PATIENT_ID" -> #[[1, "PATIENT_ID"]],
+    "LASTNAME" -> #[[1, "LASTNAME"]],
+    "VISIT_DATE" -> If[DeleteMissing[#[[All, "VISIT_DATE"]]] =!= {}, Max@DeleteMissing[#[[All, "VISIT_DATE"]]], Missing[]],
+    "SCORE_SUM" -> If[DeleteMissing@#[[All, "SCORE"]] =!= {}, Total@DeleteMissing@#[[All, "SCORE"]], Missing[]],
+    "SCORE_AVG" -> If[DeleteMissing@#[[All, "SCORE"]] =!= {}, Mean@DeleteMissing@#[[All, "SCORE"]], Missing[]]|> & /@
+  gr // Dataset
--- a/Task/Merge-and-aggregate-datasets/Mercury/merge-and-aggregate-datasets.mercury
+++ b/Task/Merge-and-aggregate-datasets/Mercury/merge-and-aggregate-datasets.mercury
@ -0,0 +1,71 @@
+:- module rosetta.
+
+:- interface.
+:- import_module io.
+:- pred main(io::di, io::uo) is det.
+
+:- implementation.
+:- import_module list, int, float, string, maybe, solutions.
+
+:- pred patient(int::out, string::out) is multi.
+patient(1001, "Hopper").
+patient(4004, "Wirth").
+patient(3003, "Kemeny").
+patient(2002, "Gosling").
+patient(5005, "Kurtz").
+
+:- func nan = float.
+nan = det_to_float("NaN").
+
+:- type maybe_date ---> date(year::int, month::int, day::int); no.
+
+:- pred visit(int::out, maybe_date::out, float::out) is multi.
+visit(2002, date(2020,09,10), 6.8).
+visit(1001, date(2020,09,17), 5.5).
+visit(4004, date(2020,09,24), 8.4).
+visit(2002, date(2020,10,08), nan).
+visit(1001, no, 6.6).
+visit(3003, date(2020,11,12), nan).
+visit(4004, date(2020,11,05), 7.0).
+visit(1001, date(2020,11,19), 5.3).
+
+%% Utilities
+:- pred bag_aggr(pred(T)::(pred(out) is nondet), pred(T,U,U)::pred(in,in,out) is det,
+		 U::in, U::out) is det.
+:- pred bag_count(pred(T)::(pred(out) is nondet), int::out) is det.
+:- pred bag_sum(pred(float)::(pred(out) is nondet), float::out) is det.
+:- pred bag_avg(pred(float)::(pred(out) is nondet), float::out) is det.
+:- pred bag_max(pred(T)::(pred(out) is nondet), T::in, T::out) is det.
+:- pred bag_max_date(pred(maybe_date)::(pred(out) is nondet), maybe_date::out) is det.
+bag_aggr(Predicate, Aggregator, Initial, Result) :-
+    promise_equivalent_solutions[Result] (
+	unsorted_aggregate(Predicate, Aggregator, Initial, Result)).
+bag_count(Predicate, Count) :-
+    bag_aggr(Predicate, (pred(_X::in,Y::in,Z::out) is det :- Z = Y+1), 0, Count).
+bag_sum(Predicate, Sum) :-
+    bag_aggr(Predicate, (pred(X::in,Y::in,Z::out) is det :- Z = X+Y), 0.0, Sum).
+bag_avg(Predicate, Avg) :-
+    bag_count(Predicate, N),
+    bag_sum(Predicate, Sum),
+    (if N = 0 then Avg = nan else Avg = Sum/float(N)).
+bag_max(Predicate, Initial, Max) :-
+    bag_aggr(Predicate,
+	     (pred(X::in,Y::in,Z::out) is det :-
+		  compare(R,X,Y),
+		  (if R = (>) then Z = X else Z = Y)),
+	     Initial, Max).
+bag_max_date(Predicate, MaxDate) :-
+    bag_max(Predicate, date(0,0,0), MaxDate1),
+    (if MaxDate1 = date(0,0,0) then MaxDate = no else MaxDate = MaxDate1).
+
+main(!IO) :-
+    print_line("{Id, Lastname, SumScores, AvgScores, MaxDate}:", !IO),
+    aggregate((pred({Id,Lastname,Sum,Avg,MaxDate}::out) is nondet :-
+	           patient(Id,Lastname),
+	           Scores = (pred(Score::out) is nondet :- visit(Id,_,Score), \+is_nan(Score)),
+	           bag_avg(Scores, Avg),
+	  	       bag_sum(Scores, Sum),
+	           Dates = (pred(Date::out) is nondet :- visit(Id,Date,_), Date\=no),
+	           bag_max_date(Dates, MaxDate)),
+	      print_line,
+	      !IO).
--- a/Task/Merge-and-aggregate-datasets/Nim/merge-and-aggregate-datasets-1.nim
+++ b/Task/Merge-and-aggregate-datasets/Nim/merge-and-aggregate-datasets-1.nim
@ -0,0 +1,53 @@
+import algorithm, parsecsv, strformat, strutils, tables
+
+const NoValue = -1.0
+
+type
+
+  Names = OrderedTable[Positive, string]      # Mapping id -> last name.
+
+  Visit = tuple[date: string; score: float]
+  Visits = Table[Positive, seq[Visit]]        # Mapping id -> list of visits.
+
+
+proc readNames(path: string): Names =
+  ## Read the records (id, lastname) from the CSV file and fill a Names table.
+  var parser: CsvParser
+  parser.open(path)
+  parser.readHeaderRow()
+  while parser.readRow():
+    let id = parser.row[0].parseInt
+    let name = parser.row[1]
+    result[id] = name
+
+proc readVisits(path: string): Visits =
+  ## Read the records (id, date, score) from the CSV file and fill a Visits table.
+  var parser: CsvParser
+  parser.open(path)
+  parser.readHeaderRow()
+  while parser.readRow():
+    let id = parser.row[0].parseInt
+    let date = parser.row[1]
+    let score = if parser.row[2].len == 0: NoValue else: parser.row[2].parseFloat
+    result.mgetOrPut(id, @[]).add (date, score)
+
+
+var
+  names = readNames("patients1.csv")
+  visits = readVisits("patients2.csv")
+
+names.sort(system.cmp)
+
+echo "| PATIENT_ID |  LASTNAME  | LAST_VISIT |  SCORE_SUM | SCORE_AVG |"
+for (id, name) in names.pairs:
+  let visitList = visits.getOrDefault(id).sorted()
+  let lastVisit = if visitList.len == 0: "" else: visitList[^1].date
+  var sum = 0.0
+  var count = 0
+  for visit in visitList:
+    if visit.score != NoValue:
+      sum += visit.score
+      inc count
+  let scoreSum = if count == 0: "" else: &"{sum:>4.1f}"
+  let scoreAvg = if count == 0: "" else: &"{sum / count.toFloat: >4.2f}"
+  echo &"| {id:^10} | {name:^10} | {lastVisit:^10} | {scoreSum:>7}    | {scoreAvg:>6}    |"
--- a/Task/Merge-and-aggregate-datasets/Nim/merge-and-aggregate-datasets-2.nim
+++ b/Task/Merge-and-aggregate-datasets/Nim/merge-and-aggregate-datasets-2.nim
@ -0,0 +1,53 @@
+import parseCsv, db_sqlite, sequtils, strutils
+
+const FNames = ["patients1.csv",  "patients2.csv"]
+
+proc createTableHeaders(conn: DbConn) =
+    conn.exec(sql"CREATE TABLE names(PATIENT_ID INT, LASTNAME TEXT);")
+    conn.exec(sql"CREATE TABLE visits(PATIENT_ID INT, VISIT_DATE DATE, SCORE NUMERIC(4,1));")
+
+
+proc fillTables(dbc: DbConn) =
+  for idx, fname in FNames:
+    dbc.exec(sql"BEGIN")
+    var parser: CsvParser
+    parser.open(fname)
+    parser.readHeaderRow()
+    while parser.readRow():
+      if idx == 0:  # "names" table.
+        dbc.exec(sql"INSERT INTO names VALUES (?, ?);", parser.row)
+      else:         # "visits" table
+        dbc.exec(sql"INSERT INTO visits VALUES (?, ?, ?);", parser.row)
+    dbc.exec(sql"COMMIT")
+
+
+proc joinTablesAndGroup(dbc: DbConn): seq[Row] =
+  dbc.exec(sql"""CREATE TABLE answer AS
+                   SELECT
+                     names.PATIENT_ID,
+                     names.LASTNAME,
+                     MAX(VISIT_DATE) AS LAST_VISIT,
+                     SUM(SCORE) AS SCORE_SUM,
+                     CAST(AVG(SCORE) AS DECIMAL(10,2)) AS SCORE_AVG
+                   FROM
+                     names
+                     LEFT JOIN visits
+                       ON visits.PATIENT_ID = names.PATIENT_ID
+                   GROUP BY
+                     names.PATIENT_ID,
+                     names.LASTNAME
+                   ORDER BY
+                     names.PATIENT_ID;""")
+  result = dbc.getAllRows(sql"SELECT * FROM ANSWER")
+
+# Build the database and execute the request to get the result.
+let dbc = open(":memory:", "", "", "")
+dbc.createTableHeaders()
+dbc.fillTables()
+let result = dbc.joinTablesAndGroup()
+dbc.close()
+
+# Print the result.
+echo "| PATIENT_ID |  LASTNAME  | LAST_VISIT |  SCORE_SUM | SCORE_AVG |"
+for row in result:
+  echo "| " & row.mapit(it.center(10)).join(" | ") & '|'
--- a/Task/Merge-and-aggregate-datasets/Perl/merge-and-aggregate-datasets.pl
+++ b/Task/Merge-and-aggregate-datasets/Perl/merge-and-aggregate-datasets.pl
@ -0,0 +1,37 @@
+#!/usr/bin/perl
+my $fmt = '| %-11s' x 5 . "|\n";
+printf $fmt, qw( PATIENT_ID LASTNAME LAST_VISIT SCORE_SUM SCORE_AVG);
+my ($names, $visits) = do { local $/; split /^\n/m, <DATA> };
+my %score;
+for ( $visits =~ /^\d.*/gm )
+  {
+  my ($id, undef, $score) = split /,/;
+  $score{$id} //= ['', ''];
+  $score and $score{$id}[0]++, $score{$id}[1] += $score;
+  }
+for ( sort $names =~ /^\d.*/gm )
+  {
+  my ($id, $name) = split /,/;
+  printf $fmt, $id, $name, ( sort $visits =~ /^$id,(.*?),/gm, '' )[-1],
+    $score{$id}[0]
+      ? ( $score{$id}[1], $score{$id}[1] / $score{$id}[0])
+      : ('', '');
+  }
+
+__DATA__
+PATIENT_ID,LASTNAME
+1001,Hopper
+4004,Wirth
+3003,Kemeny
+2002,Gosling
+5005,Kurtz
+
+PATIENT_ID,VISIT_DATE,SCORE
+2002,2020-09-10,6.8
+1001,2020-09-17,5.5
+4004,2020-09-24,8.4
+2002,2020-10-08,
+1001,,6.6
+3003,2020-11-12,
+4004,2020-11-05,7.0
+1001,2020-11-19,5.3
--- a/Task/Merge-and-aggregate-datasets/Phix/merge-and-aggregate-datasets.phix
+++ b/Task/Merge-and-aggregate-datasets/Phix/merge-and-aggregate-datasets.phix
@ -0,0 +1,59 @@
+(phixonline)-->
+ <span style="color: #008080;">constant</span> <span style="color: #000000;">patients_txt</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">split</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"""
+ PATIENT_ID,LASTNAME
+ 1001,Hopper
+ 4004,Wirth
+ 3003,Kemeny
+ 2002,Gosling
+ 5005,Kurtz"""</span><span style="color: #0000FF;">,</span><span style="color: #008000;">'\n'</span><span style="color: #0000FF;">),</span>
+          <span style="color: #000000;">visits_txt</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">split</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"""
+ PATIENT_ID,VISIT_DATE,SCORE
+ 2002,2020-09-10,6.8
+ 1001,2020-09-17,5.5
+ 4004,2020-09-24,8.4
+ 2002,2020-10-08,
+ 1001,,6.6
+ 3003,2020-11-12,
+ 4004,2020-11-05,7.0
+ 1001,2020-11-19,5.3"""</span><span style="color: #0000FF;">,</span><span style="color: #008000;">'\n'</span><span style="color: #0000FF;">)</span>
+ <span style="color: #000080;font-style:italic;">--or, assuming these files contain exactly the same actual raw text,
+ --    and the use of GT_LF_STRIPPED is instead of above split('\n'):
+ --constant patients_txt = get_text("patients.csv",GT_LF_STRIPPED),
+ --         visits_txt   = get_text("visits.csv",GT_LF_STRIPPED)</span>
+
+ <span style="color: #008080;">function</span> <span style="color: #000000;">sap</span><span style="color: #0000FF;">(</span><span style="color: #004080;">string</span> <span style="color: #000000;">s</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">return</span> <span style="color: #7060A8;">split</span><span style="color: #0000FF;">(</span><span style="color: #000000;">s</span><span style="color: #0000FF;">,</span><span style="color: #008000;">','</span><span style="color: #0000FF;">,</span><span style="color: #004600;">false</span><span style="color: #0000FF;">)&{</span><span style="color: #008000;">""</span><span style="color: #0000FF;">,</span><span style="color: #000000;">0</span><span style="color: #0000FF;">,</span><span style="color: #000000;">0</span><span style="color: #0000FF;">}</span> <span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
+ <span style="color: #008080;">function</span> <span style="color: #000000;">svp</span><span style="color: #0000FF;">(</span><span style="color: #004080;">string</span> <span style="color: #000000;">s</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">return</span> <span style="color: #7060A8;">split</span><span style="color: #0000FF;">(</span><span style="color: #000000;">s</span><span style="color: #0000FF;">,</span><span style="color: #008000;">','</span><span style="color: #0000FF;">,</span><span style="color: #004600;">false</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
+ <span style="color: #004080;">sequence</span> <span style="color: #000000;">patient_data</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">sort</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">apply</span><span style="color: #0000FF;">(</span><span style="color: #000000;">patients_txt</span><span style="color: #0000FF;">[</span><span style="color: #000000;">2</span><span style="color: #0000FF;">..$],</span><span style="color: #000000;">sap</span><span style="color: #0000FF;">)),</span>
+          <span style="color: #000000;">visit_data</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">sort_columns</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">apply</span><span style="color: #0000FF;">(</span><span style="color: #000000;">visits_txt</span><span style="color: #0000FF;">[</span><span style="color: #000000;">2</span><span style="color: #0000FF;">..$],</span><span style="color: #000000;">svp</span><span style="color: #0000FF;">),{</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,-</span><span style="color: #000000;">2</span><span style="color: #0000FF;">})</span>
+ <span style="color: #000000;">visit_data</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">append</span><span style="color: #0000FF;">(</span><span style="color: #000000;">visit_data</span><span style="color: #0000FF;">,{</span><span style="color: #008000;">""</span><span style="color: #0000FF;">,</span><span style="color: #008000;">""</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"0"</span><span style="color: #0000FF;">})</span> <span style="color: #000080;font-style:italic;">-- (add a sentinel)</span>
+ <span style="color: #004080;">string</span> <span style="color: #000000;">last_id</span> <span style="color: #0000FF;">=</span> <span style="color: #008000;">""</span><span style="color: #0000FF;">,</span><span style="color: #7060A8;">id</span><span style="color: #0000FF;">,</span><span style="color: #000000;">name</span><span style="color: #0000FF;">,</span><span style="color: #000000;">dt</span><span style="color: #0000FF;">,</span><span style="color: #000000;">scstr</span><span style="color: #0000FF;">,</span><span style="color: #000000;">avstr</span>
+ <span style="color: #004080;">atom</span> <span style="color: #000000;">score</span><span style="color: #0000FF;">,</span><span style="color: #000000;">score_total</span><span style="color: #0000FF;">,</span><span style="color: #000000;">average</span>
+ <span style="color: #004080;">integer</span> <span style="color: #000000;">visit_count</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">0</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">pdx</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">1</span>
+ <span style="color: #008080;">for</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">visit_data</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">do</span>
+     <span style="color: #0000FF;">{</span><span style="color: #7060A8;">id</span><span style="color: #0000FF;">,</span><span style="color: #000000;">dt</span><span style="color: #0000FF;">,</span><span style="color: #000000;">scstr</span><span style="color: #0000FF;">}</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">visit_data</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">]</span>
+     <span style="color: #000000;">score</span> <span style="color: #0000FF;">=</span> <span style="color: #008080;">iff</span><span style="color: #0000FF;">(</span><span style="color: #000000;">scstr</span><span style="color: #0000FF;">=</span><span style="color: #008000;">""</span><span style="color: #0000FF;">?</span><span style="color: #000000;">0</span><span style="color: #0000FF;">:</span><span style="color: #7060A8;">scanf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">scstr</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"%f"</span><span style="color: #0000FF;">)[</span><span style="color: #000000;">1</span><span style="color: #0000FF;">][</span><span style="color: #000000;">1</span><span style="color: #0000FF;">])</span>
+     <span style="color: #008080;">if</span> <span style="color: #7060A8;">id</span><span style="color: #0000FF;">!=</span><span style="color: #000000;">last_id</span> <span style="color: #008080;">then</span>
+         <span style="color: #008080;">if</span> <span style="color: #000000;">visit_count</span> <span style="color: #008080;">then</span>
+             <span style="color: #000000;">average</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">score_total</span><span style="color: #0000FF;">/</span><span style="color: #000000;">visit_count</span>
+             <span style="color: #000000;">patient_data</span><span style="color: #0000FF;">[</span><span style="color: #000000;">pdx</span><span style="color: #0000FF;">][</span><span style="color: #000000;">4</span><span style="color: #0000FF;">..</span><span style="color: #000000;">5</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">score_total</span><span style="color: #0000FF;">,</span><span style="color: #000000;">average</span><span style="color: #0000FF;">}</span>
+         <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
+         <span style="color: #008080;">if</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">visit_data</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">then</span> <span style="color: #008080;">exit</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span> <span style="color: #000080;font-style:italic;">-- (sentinel)</span>
+         <span style="color: #000000;">score_total</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">score</span>
+         <span style="color: #000000;">visit_count</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">(</span><span style="color: #000000;">score</span><span style="color: #0000FF;">!=</span><span style="color: #000000;">0</span><span style="color: #0000FF;">)</span>
+         <span style="color: #008080;">while</span> <span style="color: #7060A8;">id</span><span style="color: #0000FF;">!=</span><span style="color: #000000;">patient_data</span><span style="color: #0000FF;">[</span><span style="color: #000000;">pdx</span><span style="color: #0000FF;">][</span><span style="color: #000000;">1</span><span style="color: #0000FF;">]</span> <span style="color: #008080;">do</span> <span style="color: #000000;">pdx</span> <span style="color: #0000FF;">+=</span> <span style="color: #000000;">1</span> <span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
+         <span style="color: #000000;">patient_data</span><span style="color: #0000FF;">[</span><span style="color: #000000;">pdx</span><span style="color: #0000FF;">][</span><span style="color: #000000;">3</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">dt</span>
+         <span style="color: #000000;">last_id</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">id</span>
+     <span style="color: #008080;">elsif</span> <span style="color: #000000;">score</span><span style="color: #0000FF;">!=</span><span style="color: #000000;">0</span> <span style="color: #008080;">then</span>
+         <span style="color: #000000;">score_total</span> <span style="color: #0000FF;">+=</span> <span style="color: #000000;">score</span>
+         <span style="color: #000000;">visit_count</span> <span style="color: #0000FF;">+=</span> <span style="color: #000000;">1</span>
+     <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
+ <span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
+ <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"| PATIENT_ID | LASTNAME | LAST_VISIT |  SCORE_SUM | SCORE_AVG |\n"</span><span style="color: #0000FF;">)</span>
+ <span style="color: #008080;">for</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">patient_data</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">do</span>
+     <span style="color: #0000FF;">{</span><span style="color: #7060A8;">id</span><span style="color: #0000FF;">,</span><span style="color: #000000;">name</span><span style="color: #0000FF;">,</span><span style="color: #000000;">dt</span><span style="color: #0000FF;">,</span><span style="color: #000000;">score</span><span style="color: #0000FF;">,</span><span style="color: #000000;">average</span><span style="color: #0000FF;">}</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">patient_data</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">]</span>
+     <span style="color: #000000;">scstr</span> <span style="color: #0000FF;">=</span> <span style="color: #008080;">iff</span><span style="color: #0000FF;">(</span><span style="color: #000000;">score</span><span style="color: #0000FF;">=</span><span style="color: #000000;">0</span><span style="color: #0000FF;">?</span><span style="color: #008000;">""</span><span style="color: #0000FF;">:</span><span style="color: #7060A8;">sprintf</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"%4.1f"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">score</span><span style="color: #0000FF;">))</span>
+     <span style="color: #000000;">avstr</span> <span style="color: #0000FF;">=</span> <span style="color: #008080;">iff</span><span style="color: #0000FF;">(</span><span style="color: #000000;">average</span><span style="color: #0000FF;">=</span><span style="color: #000000;">0</span><span style="color: #0000FF;">?</span><span style="color: #008000;">""</span><span style="color: #0000FF;">:</span><span style="color: #7060A8;">sprintf</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"%4.2f"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">average</span><span style="color: #0000FF;">))</span>
+     <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"| %-10s |  %-7s | %10s |  %-9s | %-9s |\n"</span><span style="color: #0000FF;">,</span>
+             <span style="color: #0000FF;">{</span><span style="color: #7060A8;">id</span><span style="color: #0000FF;">,</span><span style="color: #000000;">name</span><span style="color: #0000FF;">,</span><span style="color: #000000;">dt</span><span style="color: #0000FF;">,</span><span style="color: #000000;">scstr</span><span style="color: #0000FF;">,</span><span style="color: #000000;">avstr</span><span style="color: #0000FF;">})</span>
+ <span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
+<!--
--- a/Task/Merge-and-aggregate-datasets/Prolog/merge-and-aggregate-datasets-1.pro
+++ b/Task/Merge-and-aggregate-datasets/Prolog/merge-and-aggregate-datasets-1.pro
@ -0,0 +1,36 @@
+patient(1001,'Hopper').
+patient(4004,'Wirth').
+patient(3003,'Kemeny').
+patient(2002,'Gosling').
+patient(5005,'Kurtz').
+
+visit(2002,'2020-09-10',6.8).
+visit(1001,'2020-09-17',5.5).
+visit(4004,'2020-09-24',8.4).
+visit(2002,'2020-10-08',nan).
+visit(1001,'',6.6).
+visit(3003,'2020-11-12',nan).
+visit(4004,'2020-11-05',7.0).
+visit(1001,'2020-11-19',5.3).
+
+summaryDates(Id, Lastname, LastDate) :-
+     aggregate(max(Ts),
+	       Score^Date^(visit(Id, Date, Score), Date \= '', parse_time(Date, iso_8601, Ts)),
+	       MaxTs),
+     format_time(atom(LastDate), '%Y-%m-%d', MaxTs),
+     patient(Id,Lastname).
+
+summaryScores(Id, Lastname, Sum, Mean) :-
+     aggregate(r(sum(Score),count), Date^(visit(Id, Date, Score), Score \= nan), r(Sum,Count)),
+     patient(Id,Lastname),
+     Mean is Sum/Count.
+
+test :-
+    summaryDates(Id, Lastname, LastDate),
+    writeln(summaryDates(Id, Lastname, LastDate)),
+    fail.
+
+test :-
+    summaryScores(Id, Lastname, ScoreSum, ScoreMean),
+    writeln(summaryScores(Id, Lastname, ScoreSum, ScoreMean)),
+    fail.
--- a/Task/Merge-and-aggregate-datasets/Prolog/merge-and-aggregate-datasets-2.pro
+++ b/Task/Merge-and-aggregate-datasets/Prolog/merge-and-aggregate-datasets-2.pro
@ -0,0 +1,49 @@
+:- import bagMax/2, bagCount/2, bagSum/2, bagReduce/4 from aggregs.
+:- import julian_date/7, date_string/3 from iso8601.
+:- import load_csv/2, add_cvt_type_hook/2 from proc_files.
+
+?- add_cvt_type_hook(date,date_converter(_,_)).
+
+date_converter(Atom,Date) :- date_string('YYYY-MM-DD',Date,Atom).
+
+:- load_csv('visit.csv',visit(integer,date,float)).
+:- load_csv('patient.csv',patient(integer,atom)).
+
+is_nan(Number) :- X is Number, X =\= Number.
+
+summaryDates(Id, Lastname, LastDate) :-
+    bagMax(date_number(Id), LastDateNumber),
+    patient(Id,Lastname),
+    julian_date(LastDateNumber, Y, M, D, _, _, _),
+    date_converter(LastDate, date(Y,M,D)).
+
+summaryScores(Id, Lastname, Sum, Mean) :-
+    bagSum(scores(Id), Sum),
+    bagCount(scores(Id), Count),
+    Mean is Sum/Count,
+    patient(Id,Lastname).
+
+test :-
+    summaryDates(Id,Lastname,LastDate),
+    writeln(summaryDates(Id,Lastname,LastDate)), fail.
+
+test :-
+    summaryScores(Id, Lastname, ScoreSum, ScoreMean),
+    writeln(summaryScores(Id, Lastname, ScoreSum, ScoreMean)), fail.
+
+/* Put hilog declarations together */
+
+date_number(Id)(Number) :-
+    visit(Id, date(Y,M,D), _),
+    julian_date(Number, Y, M, D, _, _, _).
+		
+scores(Id)(Score) :-
+    visit(Id, _, Score),
+    \+is_nan(Score).
+
+:- hilog maximum.
+maximum(X,Y,Z) :- X @> Y -> Z=X ; Z=Y.
+:- hilog sum.
+sum(X,Y,Z) :- Z is X+Y.
+:- hilog successor.
+successor(X,_Y,Z) :- Z is X+1.
--- a/Task/Merge-and-aggregate-datasets/PureBasic/merge-and-aggregate-datasets.basic
+++ b/Task/Merge-and-aggregate-datasets/PureBasic/merge-and-aggregate-datasets.basic
@ -0,0 +1,61 @@
+Structure Person
+  Name$
+EndStructure
+
+Structure Visits
+  Datum$
+  Score$
+EndStructure
+
+Structure Merge
+  Patient.Person
+  List PVisit.Visits()
+EndStructure
+
+NewMap P.Merge()
+NewList ID$()
+
+If ReadFile(1,"./Data/patients.csv")=0 : End 1 : EndIf
+header=1
+While Not Eof(1)
+  buf1$=ReadString(1)
+  If header=1 : header=0 : Continue : EndIf
+  bufId$=StringField(buf1$,1,",")
+  P(bufId$)\Patient\Name$=StringField(buf1$,2,",")
+  AddElement(ID$()) : ID$()=bufId$
+Wend
+CloseFile(1)
+
+If ReadFile(2,"./Data/visits.csv")=0 : End 2 : EndIf
+header=1
+While Not Eof(2)
+  buf1$=ReadString(2)
+  If header=1 : header=0 : Continue : EndIf
+  bufId$=StringField(buf1$,1,",")
+  AddElement(P(bufId$)\PVisit())
+  P(bufId$)\PVisit()\Datum$=StringField(buf1$,2,",")
+  P(bufId$)\PVisit()\Score$=StringField(buf1$,3,",")
+Wend
+CloseFile(2)
+
+If OpenConsole()=0 : End 3 : EndIf
+SortList(ID$(),#PB_Sort_Ascending)
+PrintN("| PATIENT_ID | LASTNAME | LAST_VISIT | SCORE_SUM | SCORE_AVG |")
+ForEach ID$()
+  Print("| "+LSet(ID$(),11))
+  Print("| "+LSet(P(ID$())\Patient\Name$,9)+"|")
+  SortStructuredList(P(ID$())\PVisit(),#PB_Sort_Ascending,OffsetOf(Visits\Datum$),TypeOf(Visits\Datum$))
+  ForEach P(ID$())\PVisit()
+    scs.f+ValF(p(ID$())\PVisit()\Score$) : c+Bool(ValF(p(ID$())\PVisit()\Score$))
+  Next
+  If LastElement(P(ID$())\PVisit())
+    sca.f=scs/c
+    Print(" "+LSet(P(ID$())\PVisit()\Datum$,10)+" |")
+    Print(RSet(StrF(scs,1),10)+" |")
+    If Not IsNAN(sca) : Print(RSet(StrF(sca,2),10)+" |") : Else : Print(Space(11)+"|") : EndIf
+  Else
+    Print(Space(12)+"|"+Space(11)+"|"+Space(11)+"|")
+  EndIf
+  PrintN("") : scs=0 : c=0
+Next
+Input()
--- a/Task/Merge-and-aggregate-datasets/Python/merge-and-aggregate-datasets-1.py
+++ b/Task/Merge-and-aggregate-datasets/Python/merge-and-aggregate-datasets-1.py
@ -0,0 +1,45 @@
+# to install pandas library go to cmd prompt and type:
+# cd %USERPROFILE%\AppData\Local\Programs\Python\Python38-32\Scripts\
+# pip install pandas
+import pandas as pd
+
+# load data from csv files
+df_patients = pd.read_csv (r'patients.csv', sep = ",", decimal=".")
+df_visits = pd.read_csv (r'visits.csv', sep = ",", decimal=".")
+
+''' # load data hard coded, create data frames
+import io
+str_patients = """PATIENT_ID,LASTNAME
+1001,Hopper
+4004,Wirth
+3003,Kemeny
+2002,Gosling
+5005,Kurtz
+"""
+df_patients = pd.read_csv(io.StringIO(str_patients), sep = ",", decimal=".")
+str_visits = """PATIENT_ID,VISIT_DATE,SCORE
+2002,2020-09-10,6.8
+1001,2020-09-17,5.5
+4004,2020-09-24,8.4
+2002,2020-10-08,
+1001,,6.6
+3003,2020-11-12,
+4004,2020-11-05,7.0
+1001,2020-11-19,5.3
+"""
+df_visits = pd.read_csv(io.StringIO(str_visits), sep = ",", decimal=".")
+'''
+
+# typecast from string to datetime so .agg can 'max' it
+df_visits['VISIT_DATE'] = pd.to_datetime(df_visits['VISIT_DATE'])
+
+# merge on PATIENT_ID
+df_merge = df_patients.merge(df_visits, on='PATIENT_ID', how='left')
+
+# groupby is an intermediate object
+df_group = df_merge.groupby(['PATIENT_ID','LASTNAME'], as_index=False)
+
+# note: you can use 'sum' instead of the lambda function but that returns NaN as 0 (zero)
+df_result = df_group.agg({'VISIT_DATE': 'max', 'SCORE': [lambda x: x.sum(min_count=1),'mean']})
+
+print(df_result)
--- a/Task/Merge-and-aggregate-datasets/Python/merge-and-aggregate-datasets-2.py
+++ b/Task/Merge-and-aggregate-datasets/Python/merge-and-aggregate-datasets-2.py
@ -0,0 +1,36 @@
+import csv
+
+fnames = 'patients.csv  patients_visits.csv'.split()
+
+def csv2list(fname):
+    with open(fname) as f:
+        rows = list(csv.reader(f))
+    return rows
+
+patients, visits = data = [csv2list(fname) for fname in fnames]
+result = [record.copy() for record in patients]
+result[1:] = sorted(result[1:])
+#%%
+result[0].append('LAST_VISIT')
+last = {p: vis for p, vis, *score in visits[1:]}
+for record in result[1:]:
+    p = record[0]
+    record.append(last.get(p, ''))
+#%%
+result[0] += ['SCORE_SUM', 'SCORE_AVG']
+n = {p: 0 for p, *_ in patients[1:]}
+tot = n.copy()
+for record in visits[1:]:
+    p, _, score = record
+    if score:
+        n[p] += 1
+        tot[p] += float(score)
+for record in result[1:]:
+    p = record[0]
+    if n[p]:
+        record += [f"{tot[p]:5.1f}", f"{tot[p] / n[p]:5.2f}"]
+    else:
+        record += ['', '']
+#%%
+for record in result:
+    print(f"| {' | '.join(f'{r:^10}' for r in record)} |")
--- a/Task/Merge-and-aggregate-datasets/Python/merge-and-aggregate-datasets-3.py
+++ b/Task/Merge-and-aggregate-datasets/Python/merge-and-aggregate-datasets-3.py
@ -0,0 +1,65 @@
+import sqlite3
+import csv
+
+
+fnames = 'patients.csv  patients_visits.csv'.split()
+conn = sqlite3.connect(":memory:")
+#%%
+
+def create_table_headers(conn):
+    curs = conn.cursor()
+    curs.execute('''
+      CREATE TABLE patients(PATIENT_ID INT, LASTNAME TEXT);
+    ''')
+    curs.execute('''
+      CREATE TABLE patients_visits(PATIENT_ID INT, VISIT_DATE DATE, SCORE NUMERIC(4,1));
+    ''')
+    conn.commit()
+
+def fill_tables(conn, fnames):
+    curs = conn.cursor()
+    for fname in fnames:
+        with open(fname) as f:
+            tablename = fname.replace('.csv', '')
+            #
+            csvdata = csv.reader(f)
+            header = next(csvdata)
+            fields = ','.join('?' for _ in header)
+            for row in csvdata:
+                row = [(None if r == '' else r) for r in row]
+                curs.execute(f"INSERT INTO {tablename} VALUES ({fields});", row)
+    conn.commit()
+
+def join_tables_and_group(conn):
+    curs = conn.cursor()
+    curs.execute('''
+CREATE TABLE answer AS
+    SELECT
+    	patients.PATIENT_ID,
+    	patients.LASTNAME,
+    	MAX(VISIT_DATE) AS LAST_VISIT,
+    	SUM(SCORE) AS SCORE_SUM,
+    	CAST(AVG(SCORE) AS DECIMAL(10,2)) AS SCORE_AVG
+    FROM
+    	patients
+    	LEFT JOIN patients_visits
+    		ON patients_visits.PATIENT_ID = patients.PATIENT_ID
+    GROUP BY
+    	patients.PATIENT_ID,
+    	patients.LASTNAME
+    ORDER BY
+    	patients.PATIENT_ID;
+        ''')
+    curs.execute('''
+SELECT * FROM answer;
+        ''')
+    conn.commit()
+    rows = list(curs.fetchall())
+    headers = tuple(d[0] for d in curs.description)
+    return [headers] + rows
+
+create_table_headers(conn)
+fill_tables(conn, fnames)
+result = join_tables_and_group(conn)
+for record in result:
+    print(f"| {' | '.join(f'{str(r):^10}' for r in record)} |")
--- a/Task/Merge-and-aggregate-datasets/R/merge-and-aggregate-datasets.r
+++ b/Task/Merge-and-aggregate-datasets/R/merge-and-aggregate-datasets.r
@ -0,0 +1,42 @@
+# load data from csv files
+# setwd("C:\Temp\csv\")
+# df_patient <- read.csv(file="patients.csv", header = TRUE, sep = ",")
+# df_visits <- read.csv(file="visits.csv", header = TRUE, sep = ",", dec = ".", colClasses=c("character","character","numeric"))
+
+# load data hard coded, create data frames
+df_patient <- read.table(text = "
+PATIENT_ID,LASTNAME
+1001,Hopper
+4004,Wirth
+3003,Kemeny
+2002,Gosling
+5005,Kurtz
+", header = TRUE, sep = ",") #  character fields so no need for extra parameters colClasses etc.
+
+df_visits <- read.table(text = "
+PATIENT_ID,VISIT_DATE,SCORE
+2002,2020-09-10,6.8
+1001,2020-09-17,5.5
+4004,2020-09-24,8.4
+2002,2020-10-08,
+1001,,6.6
+3003,2020-11-12,
+4004,2020-11-05,7.0
+1001,2020-11-19,5.3
+", header = TRUE, dec = ".", sep = ",", colClasses=c("character","character","numeric"))
+
+# aggregate visit date and scores
+df_agg <- data.frame(
+  cbind(
+    PATIENT_ID = names(tapply(df_visits$VISIT_DATE, list(df_visits$PATIENT_ID), max, na.rm=TRUE)),
+    last_visit = tapply(df_visits$VISIT_DATE, list(df_visits$PATIENT_ID), max, na.rm=TRUE),
+    score_sum = tapply(df_visits$SCORE, list(df_visits$PATIENT_ID), sum, na.rm=TRUE),
+    score_avg = tapply(df_visits$SCORE, list(df_visits$PATIENT_ID), mean, na.rm=TRUE)
+  )
+)
+
+# merge patients and aggregate dataset
+# all.x = all the non matching cases of df_patient are appended to the result as well (i.e. 'left join')
+df_result <- merge(df_patient, df_agg, by = 'PATIENT_ID', all.x = TRUE)
+
+print(df_result)
--- a/Task/Merge-and-aggregate-datasets/REXX/merge-and-aggregate-datasets.rexx
+++ b/Task/Merge-and-aggregate-datasets/REXX/merge-and-aggregate-datasets.rexx
@ -0,0 +1,81 @@
+/* REXX */
+patients='patients.csv'
+l=linein(patients)
+Parse Var l h1 ',' h2
+n=0
+idl=''
+Do n=1 By 1 While lines(patients)>0
+  l=linein(patients)
+  Parse Var l id ',' lastname.id
+  idl=idl id
+  End
+n=n-1 /* number of patients */
+visits='visits.csv'
+l=linein(visits) /* skip the header line of this file */
+h3='LAST_VISIT'
+h4='SCORE_SUM'
+h5='SCORE_AVG'
+date.=''
+score.=0
+Say '|' h1 '|' h2 '|' h3 '|' h4 '|' h5 '|'
+Do While lines(visits)>0
+  l=linein(visits)
+  Parse Var l id ',' date ',' score
+  if date>date.id Then date.id=date
+  If score>'' Then Do
+    z=score.id.0+1
+    score.id.z=score
+    score.id.0=z
+    End
+  end
+idl=wordsort(idl)
+Do While idl<>''
+  Parse Var idl id idl
+  If date.id='' Then date.id=copies(' ',10)
+  ol='|' left(id,length(h1)) '|' left(lastname.id,length(h2)),
+                             '|' left(date.id,length(h3))
+  If score.id.0=0 Then Do
+  ol=ol '|' left(' ',length(h4)) '|',
+            left(' ',length(h5)) '|'
+    score_sum=copies(' ',length(h4))
+    score_avg=copies(' ',length(h4))
+    End
+  Else Do
+    score_sum=0
+    Do j=1 To score.id.0
+      score_sum=score_sum+score.id.j
+      End
+    score_avg=score_sum/score.id.0
+    ol=ol '|' left(format(score_sum,2,1),length(h4)) '|',
+             left(format(score_avg,2,1),length(h5)) '|'
+    End
+  Say ol
+  End
+Exit
+
+wordsort: Procedure
+/**********************************************************************
+* Sort the list of words supplied as argument. Return the sorted list
+**********************************************************************/
+  Parse Arg wl
+  wa.=''
+  wa.0=0
+  Do While wl<>''
+    Parse Var wl w wl
+    Do i=1 To wa.0
+      If wa.i>w Then Leave
+      End
+    If i<=wa.0 Then Do
+      Do j=wa.0 To i By -1
+        ii=j+1
+        wa.ii=wa.j
+        End
+      End
+    wa.i=w
+    wa.0=wa.0+1
+    End
+  swl=''
+  Do i=1 To wa.0
+    swl=swl wa.i
+    End
+  Return strip(swl)
--- a/Task/Merge-and-aggregate-datasets/Raku/merge-and-aggregate-datasets.raku
+++ b/Task/Merge-and-aggregate-datasets/Raku/merge-and-aggregate-datasets.raku
@ -0,0 +1,37 @@
+my @names = map { ( <PATIENT_ID LASTNAME> Z=> .list ).hash },
+    ( 1001, 'Hopper'  ),
+    ( 4004, 'Wirth'   ),
+    ( 3003, 'Kemeny'  ),
+    ( 2002, 'Gosling' ),
+    ( 5005, 'Kurtz'   ),
+;
+my @visits = map { ( <PATIENT_ID VISIT_DATE SCORE> Z=> .list ).hash },
+    ( 2002, '2020-09-10', 6.8 ),
+    ( 1001, '2020-09-17', 5.5 ),
+    ( 4004, '2020-09-24', 8.4 ),
+    ( 2002, '2020-10-08', Nil ),
+    ( 1001,         Nil , 6.6 ),
+    ( 3003, '2020-11-12', Nil ),
+    ( 4004, '2020-11-05', 7.0 ),
+    ( 1001, '2020-11-19', 5.3 ),
+;
+
+my %v = @visits.classify: *.<PATIENT_ID>;
+
+my @result = gather for @names -> %n {
+    my @p = %v{ %n.<PATIENT_ID> }<>;
+
+    my @dates  = @p».<VISIT_DATE>.grep: *.defined;
+    my @scores = @p».<     SCORE>.grep: *.defined;
+
+    take {
+        %n,
+        LAST_VISIT => ( @dates.max          if @dates  ),
+        SCORE_AVG  => ( @scores.sum/@scores if @scores ),
+        SCORE_SUM  => ( @scores.sum         if @scores ),
+    };
+}
+
+my @out_field_names = <PATIENT_ID LASTNAME LAST_VISIT SCORE_SUM SCORE_AVG>;
+my @rows = @result.sort(*.<PATIENT_ID>).map(*.{@out_field_names});
+say .map({$_ // ''}).fmt('%-10s', ' | ') for @out_field_names, |@rows;
--- a/Task/Merge-and-aggregate-datasets/SAS/merge-and-aggregate-datasets.sas
+++ b/Task/Merge-and-aggregate-datasets/SAS/merge-and-aggregate-datasets.sas
@ -0,0 +1,20 @@
+  %let datefmt=E8601DA10.;
+  data patient;
+      infile "patient.csv" dsd dlm=',';
+      attrib
+          id length=4
+          lastname length=$10;
+      input id lastname;
+  data visit;
+      infile "visit.csv" dsd dlm=',';
+      attrib
+          id length=4
+          date informat=&datefmt format=&datefmt
+          score length=8;
+      input id date score;
+  proc sql;
+      select * from
+          (select id, max(date) format=&datefmt as max_date, sum(score) as sum_score,
+          	avg(score) as avg_score from visit group by id)
+          natural right join patient
+          order by id;
--- a/Task/Merge-and-aggregate-datasets/SPSS/merge-and-aggregate-datasets.spss
+++ b/Task/Merge-and-aggregate-datasets/SPSS/merge-and-aggregate-datasets.spss
@ -0,0 +1,66 @@
+* set working directory to location of .csv files
+
+CD 'C:\Temp\csv\'.
+
+* load patients csv data
+
+GET DATA /TYPE=TXT
+  /FILE="patients.csv"
+  /ENCODING='UTF8'
+  /DELCASE=LINE
+  /DELIMITERS=","
+  /QUALIFIER='"'
+  /ARRANGEMENT=DELIMITED
+  /FIRSTCASE=2
+  /IMPORTCASE=ALL
+  /VARIABLES=
+PATIENT_ID F5.0
+LASTNAME A20
+.
+CACHE.
+EXECUTE.
+
+* sort cases is needed to match files
+
+SORT CASES BY PATIENT_ID (A).
+DATASET NAME Patients WINDOW=FRONT.
+
+* load visits csv data
+
+GET DATA /TYPE=TXT
+  /FILE="visit.csv"
+  /ENCODING='UTF8'
+  /DELCASE=LINE
+  /DELIMITERS=","
+  /QUALIFIER='"'
+  /ARRANGEMENT=DELIMITED
+  /FIRSTCASE=2
+  /IMPORTCASE=ALL
+  /VARIABLES=
+PATIENT_ID F5.0
+VISIT_DATE SDATE10
+SCORE F4.1
+.
+CACHE.
+EXECUTE.
+
+* sort cases is needed, else match files will raise error "Files out of order"
+
+SORT CASES BY PATIENT_ID (A) VISIT_DATE (A).
+DATASET NAME Visits WINDOW=FRONT.
+
+* load visits csv data
+
+* merge datasets, one to many, FILE is the 'one', TABLE is 'many'
+
+MATCH FILES TABLE = Patients / FILE = Visits
+/BY PATIENT_ID.
+EXECUTE.
+
+* aggregate visit date and scores, group by and order (A)=ascending or (D)=descending
+
+AGGREGATE OUTFILE *
+/BREAK=PATIENT_ID(A)
+/last_visit = MAX(VISIT_DATE)
+/score_avg = MEAN(SCORE)
+/score_sum = SUM(SCORE).
--- a/Task/Merge-and-aggregate-datasets/SQL/merge-and-aggregate-datasets.sql
+++ b/Task/Merge-and-aggregate-datasets/SQL/merge-and-aggregate-datasets.sql
@ -0,0 +1,59 @@
+-- drop tables
+DROP TABLE IF EXISTS tmp_patients;
+DROP TABLE IF EXISTS tmp_visits;
+
+-- create tables
+CREATE TABLE tmp_patients(
+	PATIENT_ID INT,
+	LASTNAME VARCHAR(20)
+);
+
+CREATE TABLE tmp_visits(
+	PATIENT_ID INT,
+	VISIT_DATE DATE,
+	SCORE NUMERIC(4,1)
+);
+
+-- load data from csv files
+/*
+-- Note: LOAD DATA LOCAL requires `local-infile` enabled on both the client and server else you get error "#1148 command is not allowed.."
+LOAD DATA LOCAL INFILE '/home/csv/patients.csv' INTO TABLE `tmp_patients` FIELDS TERMINATED BY ',' LINES TERMINATED BY '\n' IGNORE 1 LINES;
+LOAD DATA LOCAL INFILE '/home/csv/visits.csv' INTO TABLE `tmp_visits` FIELDS TERMINATED BY ',' LINES TERMINATED BY '\n' IGNORE 1 LINES;
+*/
+
+-- load data hard coded
+INSERT INTO tmp_patients(PATIENT_ID, LASTNAME)
+VALUES
+(1001, 'Hopper'),
+(4004, 'Wirth'),
+(3003, 'Kemeny'),
+(2002, 'Gosling'),
+(5005, 'Kurtz');
+
+INSERT INTO tmp_visits(PATIENT_ID, VISIT_DATE, SCORE)
+VALUES
+(2002, '2020-09-10', 6.8),
+(1001, '2020-09-17', 5.5),
+(4004, '2020-09-24', 8.4),
+(2002, '2020-10-08', NULL),
+(1001, NULL, 6.6),
+(3003, '2020-11-12', NULL),
+(4004, '2020-11-05', 7.0),
+(1001, '2020-11-19', 5.3);
+
+-- join tables and group
+SELECT
+	p.PATIENT_ID,
+	p.LASTNAME,
+	MAX(VISIT_DATE) AS LAST_VISIT,
+	SUM(SCORE) AS SCORE_SUM,
+	CAST(AVG(SCORE) AS DECIMAL(10,2)) AS SCORE_AVG
+FROM
+	tmp_patients p
+	LEFT JOIN tmp_visits v
+		ON v.PATIENT_ID = p.PATIENT_ID
+GROUP BY
+	p.PATIENT_ID,
+	p.LASTNAME
+ORDER BY
+	p.PATIENT_ID;
--- a/Task/Merge-and-aggregate-datasets/Transd/merge-and-aggregate-datasets.transd
+++ b/Task/Merge-and-aggregate-datasets/Transd/merge-and-aggregate-datasets.transd
@ -0,0 +1,59 @@
+#lang transd
+
+MainModule: {
+
+tbl: `1001,Hopper
+4004,Wirth
+3003,Kemeny
+2002,Gosling
+5005,Kurtz`,
+
+tbl1: `
+2002,2020-09-10,6.8
+1001,2020-09-17,5.5
+4004,2020-09-24,8.4
+2002,2020-10-08,
+1001,,6.6
+3003,2020-11-12,
+4004,2020-11-05,7.0
+1001,2020-11-19,5.3`,
+
+cols: `@key_PATIENT_ID:Int,
+        LASTNAME:String,
+        VISIT_DATE:DateTime,
+        SCORE:Double,
+        SCORE_AVG:Double,
+        NUM_VISITS:Int`,
+
+Record : typealias(Tuple<Int DateTime Double>()),
+
+	_start: (λ (with base TSDBase()
+		(load-table base tbl colNames: cols)
+        (build-index base "PATIENT_ID")
+
+        (with vizs Vector<Record>()
+            (load-table vizs tbl1 :mixedTypes fieldSep: "," rowSep: "\n" )
+            (for viz in vizs do
+                (tsd-query base
+                    :update set:
+                (lambda PATIENT_ID Int() VISIT_DATE DateTime()
+                        SCORE Double() SCORE_AVG Double() NUM_VISITS Int()
+                    (+= NUM_VISITS 1)
+                    (set VISIT_DATE (get viz 1))
+                    (set SCORE (+ SCORE (get viz 2)))
+                    (set SCORE_AVG (/ SCORE NUM_VISITS)))
+            where: (lambda PATIENT_ID Int() (eq PATIENT_ID (get viz 0))))
+            ))
+
+        (with cols ["PATIENT_ID","LASTNAME","VISIT_DATE","SCORE","SCORE_AVG"]
+        (with recs (tsd-query base select: cols
+                as: [[Int(), String(), DateTime(), Double(), Double()]]
+                where: (lambda PATIENT_ID Int() true)
+                )
+                (for i in cols do (textout width: 10 i "|")) (lout "")
+                (for rec in recs do
+                    (for-each rec (λ i :Data() (textout width: 10 i "|" )))
+                    (lout ""))
+		))
+	))
+}
--- a/Task/Merge-and-aggregate-datasets/TutorialD/merge-and-aggregate-datasets.tutoriald
+++ b/Task/Merge-and-aggregate-datasets/TutorialD/merge-and-aggregate-datasets.tutoriald
@ -0,0 +1,36 @@
+BEGIN;
+  TYPE Date UNION;
+  TYPE DateValid IS {Date POSSREP {year INTEGER, month INTEGER, day INTEGER}};
+  TYPE DateNone IS {Date POSSREP {}};
+  TYPE DateUnknown IS {Date POSSREP {}};
+END;
+
+VAR patient REAL RELATION {id INT, lastname CHAR} KEY {id};
+
+INSERT patient RELATION
+{TUPLE {id 1001, lastname 'Hopper'},
+ TUPLE {id 4004, lastname 'Wirth'},
+ TUPLE {id 3003, lastname 'Kemeny'},
+ TUPLE {id 2002, lastname 'Gosling'},
+ TUPLE {id 5005, lastname 'Kurtz'}
+ };
+
+VAR visit REAL RELATION {id INT, date Date, score RATIONAL} KEY {id, date};
+
+INSERT visit RELATION
+{
+TUPLE {id 2002, date DateValid(2020,09,10), score 6.8},
+TUPLE {id 1001, date DateValid(2020,09,17), score 5.5},
+TUPLE {id 4004, date DateValid(2020,09,24), score 8.4},
+TUPLE {id 2002, date DateValid(2020,10,08), score NAN},
+TUPLE {id 1001, date DateNone(), score 6.6},
+TUPLE {id 3003, date DateValid(2020,11,12), score NAN},
+TUPLE {id 4004, date DateValid(2020,11,05), score 7.0},
+TUPLE {id 1001, date DateValid(2020,11,19), score 5.3}
+};
+
+((SUMMARIZE (visit WHERE score>0.0) BY {id}: {sumscore := SUM(score), avgscore := AVG(score)}) UNION
+ (EXTEND (patient {id} MINUS ((visit WHERE score>0.0) {id})): {sumscore := NaN, avgscore := NaN})) JOIN
+    (SUMMARIZE visit BY {id}: {maxdate := MAX(date)} UNION
+     (EXTEND (patient {id} MINUS (visit {id})): {maxdate := DateUnknown()})) JOIN
+    patient
--- a/Task/Merge-and-aggregate-datasets/Wren/merge-and-aggregate-datasets.wren
+++ b/Task/Merge-and-aggregate-datasets/Wren/merge-and-aggregate-datasets.wren
@ -0,0 +1,96 @@
+import "/fmt" for Fmt
+import "/sort" for Sort
+
+class Patient {
+    construct new(id, lastName) {
+        _id = id
+        _lastName = lastName
+        if (!__dir) __dir = {}
+        __dir[id] = lastName
+        if (!__ids) {
+            __ids = [id]
+        } else {
+            __ids.add(id)
+            Sort.insertion(__ids)
+        }
+    }
+
+    id       { _id }
+    lastName { _lastName }
+
+    // maps an id to a lastname
+    static dir { __dir }
+
+    // maintains a sorted list of ids
+    static ids { __ids }
+}
+
+class Visit {
+    construct new(id, date, score) {
+        _id = id
+        _date = date || "0000-00-00"
+        _score = score
+        if (!__dir) __dir = {}
+        if (!__dir[id]) {
+            __dir[id] = [ [_date], [score] ]
+        } else {
+            __dir[id][0].add(_date)
+            __dir[id][1].add(score)
+        }
+    }
+
+    id    { _id }
+    date  { _date }
+    score { _score }
+
+     // maps an id to lists of dates and scores
+    static dir { __dir }
+}
+
+class Merge {
+    construct new(id) {
+        _id = id
+    }
+
+    id        { _id }
+    lastName  { Patient.dir[_id] }
+    dates     { Visit.dir[_id][0] }
+    scores    { Visit.dir[_id][1] }
+    lastVisit { Sort.merge(dates)[-1] }
+
+    scoreSum  { scores.reduce(0) { |acc, s| s ? acc + s : acc } }
+    scoreAvg  { scoreSum / scores.count { |s| s } }
+
+    static print(merges) {
+        System.print("| PATIENT_ID | LASTNAME | LAST_VISIT | SCORE_SUM | SCORE_AVG |")
+        var fmt = "| $d       | $-7s  | $s | $4s      | $4s      |"
+        for (m in merges) {
+            if (Visit.dir[m.id]) {
+                var lv = (m.lastVisit != "0000-00-00") ? m.lastVisit : "          "
+                var ss = (m.scoreSum > 0) ? Fmt.f(4, m.scoreSum, 1) : "    "
+                var sa = (!m.scoreAvg.isNan) ? Fmt.f(4, m.scoreAvg, 2) : "    "
+                Fmt.print(fmt, m.id, m.lastName, lv, ss, sa)
+            } else {
+                Fmt.print(fmt, m.id, m.lastName, "          ", "    ", "    ")
+            }
+        }
+    }
+}
+
+Patient.new(1001, "Hopper")
+Patient.new(4004, "Wirth")
+Patient.new(3003, "Kemeny")
+Patient.new(2002, "Gosling")
+Patient.new(5005, "Kurtz")
+
+Visit.new(2002, "2020-09-10", 6.8)
+Visit.new(1001, "2020-09-17", 5.5)
+Visit.new(4004, "2020-09-24", 8.4)
+Visit.new(2002, "2020-10-08", null)
+Visit.new(1001,  null       , 6.6)
+Visit.new(3003, "2020-11-12", null)
+Visit.new(4004, "2020-11-05", 7.0)
+Visit.new(1001, "2020-11-19", 5.3)
+
+var merges = Patient.ids.map { |id| Merge.new(id) }.toList
+Merge.print(merges)