Array transpose implementation

Main.purs

module Main where

import Prelude

import Data.Array as A
import Data.Maybe (Maybe(..), maybe)
import Effect (Effect)
import Effect.Class.Console (log)
import TryPureScript as TryPureScript

main :: Effect Unit
main = TryPureScript.render =<< TryPureScript.withConsole do
  test [[]] []
  test [[1], [2], [3]] [[1, 2, 3]]
  test [[1], [2], [3, 4]] [[1, 2, 3], [4]]
  test [[1, 2], [3, 4], [5, 6, 7]] [[1, 3, 5], [2, 4, 6], [7]]
  test [[1, 2], [3, 4, 7], [5, 6]] [[1, 3, 5], [2, 4, 6], [7]]

test :: Array (Array Int) -> Array (Array Int) -> Effect Unit
test i o = do
  log $ "(transpose " <> (show i) <> ") == " <> show o <> " is " <> show ((transpose i) == o)


transpose :: forall a. Array (Array a) -> Array (Array a)
transpose xs = go 0 []
 where
 go :: Int -> Array (Array a) -> Array (Array a)
 go idx allArrays = case buildNext idx of
  Nothing -> allArrays
  Just next -> go (idx + 1) (A.snoc allArrays next)
  
   
 buildNext :: Int -> Maybe (Array a)
 buildNext idx = do
  xs # flip A.foldl Nothing \acc nextArr -> do
   maybe acc (\el -> Just $ maybe [el] (flip A.snoc el) acc) $ A.index nextArr idx