Data update

Task/Stem-and-leaf-plot/Erlang/stem-and-leaf-plot.erl

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+%%% ============================================================
+%%%  Stem-and-Leaf Plot in Erlang
+%%% ============================================================
+%%%  - Pure functions
+%%%  - No mutation
+%%%  - Deterministic transformations
+%%%  - Explicit functional pipeline
+%%% ============================================================
+
+-module(stem_leaf).
+-export([main/0]).
+
+%%% ============================================================
+%%% 1. Mathematical Helpers (Pure Functions)
+%%% ============================================================
+
+%% expand_number/1
+%% Conceptually expands single digit numbers to two-digit
+%% (e.g., 7 -> 07). Numerically unchanged, but included
+%% for semantic clarity.
+expand_number(N) ->
+    N.
+
+%% stem/1
+%% Returns the stem (all but the last digit).
+%% Example: 127 -> 12
+stem(N) ->
+    N div 10.
+
+%% leaf/1
+%% Returns the leaf (last digit).
+%% Example: 127 -> 7
+leaf(N) ->
+    N rem 10.
+
+%% range/2
+%% Returns a list of integers from From to To (inclusive).
+%% Used to guarantee stems 0..14 are always present.
+range(From, To) when From =< To ->
+    lists:seq(From, To).
+
+%%% ============================================================
+%%% 2. Data Transformation Pipeline
+%%% ============================================================
+
+%% build_stem_leaf/1
+%% Takes raw data and returns a list of:
+%%     [{Stem, [SortedLeaves]}, ...]
+%%
+%% Steps:
+%% 1. Expand numbers
+%% 2. Sort entire dataset
+%% 3. Generate all stems 0..14
+%% 4. Collect and sort leaves for each stem
+build_stem_leaf(Data) ->
+    Expanded = [expand_number(N) || N <- Data],
+    Sorted = lists:sort(Expanded),
+    Stems = range(0, 14),
+    [{S, sorted_leaves(S, Sorted)} || S <- Stems].
+
+%% sorted_leaves/2
+%% Filters all numbers matching a given stem
+%% Extracts leaves
+%% Sorts leaves
+sorted_leaves(StemValue, Data) ->
+    Leaves =
+        [leaf(N) || N <- Data, stem(N) =:= StemValue],
+    lists:sort(Leaves).
+
+%%% ============================================================
+%%% 3. Formatting Functions (Pure Rendering Layer)
+%%% ============================================================
+
+%% format_stem/1
+%% Formats stem as two digits (leading zero if needed).
+%% Example: 7 -> "07"
+format_stem(S) ->
+    io_lib:format("~2..0B", [S]).
+
+%% format_leaves/1
+%% Converts list of integers into space-separated string.
+%% Example: [1,3,7] -> "1 3 7"
+format_leaves([]) ->
+    "";
+format_leaves(Leaves) ->
+    string:join([integer_to_list(L) || L <- Leaves], " ").
+
+%% render_line/1
+%% Converts {Stem, Leaves} into formatted line.
+%% Example:
+%%   {12, [3,4,7]} -> "12 | 3 4 7"
+render_line({StemValue, Leaves}) ->
+    lists:flatten(
+        io_lib:format("~s | ~s",
+            [format_stem(StemValue), format_leaves(Leaves)])
+    ).
+
+%% render_plot/1
+%% Converts full stem-leaf structure into multi-line string.
+render_plot(StemLeafPairs) ->
+    Lines = [render_line(Pair) || Pair <- StemLeafPairs],
+    string:join(Lines, "\n").
+
+%%% ============================================================
+%%% 4. Program Entry Point
+%%% ============================================================
+
+main() ->
+    %% --------------------------------------------------------
+    %% Raw Dataset
+    %% --------------------------------------------------------
+    Data = [
+        12,127,28,42,39,113,42,18,44,118,44,37,113,124,37,48,127,36,29,31,
+        125,139,131,115,105,132,104,123,35,113,122,42,117,119,58,109,23,
+        105,63,27,44,105,99,41,128,121,116,125,32,61,37,127,29,113,121,
+        58,114,126,53,114,96,25,109,7,31,141,46,13,27,43,117,116,27,7,
+        68,40,31,115,124,42,128,52,71,118,117,38,27,106,33,117,116,111,
+        40,119,47,105,57,122,109,124,115,43,120,43,27,27,18,28,48,125,
+        107,114,34,133,45,120,30,127,31,116,146
+    ],
+
+    %% --------------------------------------------------------
+    %% Functional Processing Pipeline
+    %% --------------------------------------------------------
+    StemLeafStructure = build_stem_leaf(Data),
+    Plot = render_plot(StemLeafStructure),
+
+    %% --------------------------------------------------------
+    %% Output
+    %% --------------------------------------------------------
+    io:format("~s~n", [Plot]).