Posted on May 15, 2019

Pack the same elements into a list inside a list.

Again a challenge from 99 Elm problems

Convert a list to a list of lists where repeated elements of the source list are packed into sublists. Elements that are not repeated should be placed in a one element sublist.

pack [1,1,1,2,3,3,3,4,4,4,4,5,6,6] == [ [1,1,1] , [2] , [3, 3, 3] , [4, 4, 4, 4] , [5] , [6, 6] ]

Top comments (3)

Anton • May 15 '19

For now I have this. Can you guess what's wrong with this code?

pack : List a -> List (List a) pack list = List.foldr pusher [] list pusher : a -> List b -> List (List b) pusher y ys = if List.isEmpty ys then y :: ys else if y == List.head <| List.head ys then y :: List.head ys else [y] :: ys

Idan Arye • May 16 '19

Should [1, 2, 1] be converted to [[1], [2], [1]] or to [[1, 1], [2]]?

Anton • May 16 '19

To [[1], [2], [1]]