function to take every nth element from a List?

Stream: Is there code for X?

[Scott Morrison]

Presumably we have somewhere a function to take every nth element from a List. In particular I would like n=2. :-)

[Matthew Ballard]

Is there no filterIdx?

[Scott Morrison]

Doesn't appear to be.

[Eric Wieser]

You can filter list.enum

[Kyle Miller]

Is there a function that splits a list into groups of k?

The n=2 case can sometimes be useful too.

def List.pairs : List α → List (α × α)
  | x :: y :: xs => (x, y) :: xs.pairs
  | [] => []
  | _ => panic! "List.pairs given list of non-even length"