Udo Stenzel wrote:

jim burton wrote:

I want to split a string into 5 parts of equal length, with the last fifth
padded if necessary, but can't get it right - here's what I've got -


fifths s = unwords.take 5.unfoldr (Just . splitAt l) $ s ++ repeat ' '
  where l = (length s + 4) `div` 5

Okay, you win. That's the nicest answer so far, I think.

But here are solutions with a different theme altogether. They are based on groupBy, not unfoldr. I really like the new `on` function.

module Chunk where

import Data.List

(on) f g = \x y -> f (g x) (g y)

groupByIndex test xs =
    map (map snd) $ groupBy (test `on` fst) $ zip [0..] xs

-- chunk : divide the input string into n chunks of equal length (len), with padding

-- chunk1 accepts the number of chunks
chunk1 n pad xs =
    unwords $ take n $ groupByIndex ((==) `on` (`div` len)) $ xs ++ repeat pad
        where len = (length xs + n - 1) `div` n

-- chunk2 accepts the length of each chunk
chunk2 len pad xs =
    unwords $ take n $ groupByIndex ((==) `on` (`div` len)) $ xs ++ repeat pad
        where n = (length xs + len - 1) `div` len