June 2018 Update

Task/Stem-and-leaf-plot/Haskell/stem-and-leaf-plot-2.hs

@@ -0,0 +1,72 @@
+import Data.List     (groupBy, intersperse, mapAccumL, sortBy)
+import Data.Ord      (comparing)
+import Data.Function (on)
+import Control.Arrow ((&&&))
+
+-- Strings derived from integers,
+-- and split into [(initial string, final character)] tuples.
+
+xs :: [(String, Char)]
+xs = (init &&& last) . show <$> [
+      12, 127, 28, 42, 39, 113, 42, 18, 44, 118, 44, 37, 113, 124, 37, 48,
+      127, 36, 29, 31, 125, 139, 131, 115, 105, 132, 104, 123, 35, 113, 122,
+      42, 117, 119, 58, 109, 23, 105, 63, 27, 44, 105, 99, 41, 128, 121, 116,
+      125, 32, 61, 37, 127, 29, 113, 121, 58, 114, 126, 53, 114, 96, 25, 109,
+      7, 31, 141, 46, 13, 27, 43, 117, 116, 27, 7, 68, 40, 31, 115, 124, 42,
+      128, 52, 71, 118, 117, 38, 27, 106, 33, 117, 116, 111, 40, 119, 47, 105,
+      57, 122, 109, 124, 115, 43, 120, 43, 27, 27, 18, 28, 48, 125, 107,
+      114, 34, 133, 45, 120, 30, 127, 31, 116, 146
+    ]
+
+-- Re-reading the initial strings as Ints
+-- (empty strings read as 0),
+ns :: [(Int, Char)]
+ns =
+  (\x ->
+      let s = fst x
+      in ( if null s
+             then 0
+             else (read s :: Int)
+         , snd x)) <$>
+  xs
+
+-- and sorting and grouping by these initial Ints,
+-- interpreting them as data-collection bins.
+bins :: [[(Int, Char)]]
+bins =
+  groupBy (on (==) fst) (sortBy (mappend (comparing fst) (comparing snd)) ns)
+
+-- Forming bars by the ordered accumulation of final characters in each bin,
+bars :: [(Int, String)]
+bars = (fst . head &&& fmap snd) <$> bins
+
+-- and obtaining a complete series, with empty bar strings
+-- interpolated for any missing integers.
+series :: [(Int, String)]
+series =
+  (concat . snd) $
+  mapAccumL
+    (\a x ->
+        let n = fst x
+        in if a == n
+             then (a + 1, [x])
+             else (n + 1, ((\i -> (i, "")) <$> [a .. (n - 1)]) ++ [x]))
+    1
+    bars
+
+-- Assembling the series as a list of strings with right-justified indices,
+justifyRight :: Int -> Char -> String -> String
+justifyRight n c s = drop (length s) (replicate n c ++ s)
+
+plotLines :: [String]
+plotLines =
+  foldr
+    (\x a ->
+        (justifyRight 2 ' ' (show (fst x)) ++ " |  " ++ intersperse ' ' (snd x)) :
+        a)
+    []
+    series
+
+-- and passing these over to IO as a single newline-delimited string.
+main :: IO ()
+main = putStrLn $ unlines plotLines