30-seconds-of-code/snippets/split_list.md

title, tags

title	tags
split_list	list,divmod,intermediate

Splits a long list into "parts" number of smaller lists, which are as close as possible to each other in length.

• Check if parts is larger than len(lst) in order to not split the list into more parts than there are elements.
• The max(len(lst), 1) check will handle zero length lists, but parts < 1 will yield bad results.
• k = len(lst)//n -> an integer specifying the number of elements in each shorter list (i.e. the quotient).
• m = len(lst)%n -> if len(lst)/n does not equal a whole number, this equals how many "extra" elements there are (i.e. the remainder).
• In order to get n short lists, every loop iteration goes to i * k and then take the next k elements.
• If m > 0, then the early iterations will have one extra element in their list until i > m (no extra elements left).
• Return a meta-list containing all these shorter lists.

def split_list(lst: list, parts: int) -> list:
  n = min(parts, max(len(lst), 1))
  k, m = divmod(len(lst), n)
  return [lst[i * k + min(i, m):(i + 1) * k + min(i + 1, m)] for i in range(n)]

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

split_list(l, 2) # [[1, 2, 3], [4, 5, 6]]
split_list(l, 4) # [[1, 2], [3, 4], [5], [6]]
split_list(l, 9) # [[1], [2], [3], [4], [5], [6]]