Add split_list

This code comes from one of my [gists][1], but could probably be more
useful here where it might be easier to find.

[1]: https://gist.github.com/JonasAlfredsson/6e30169c5c69813651baf050dbfc7203

snippets/split_list.md

@@ -0,0 +1,29 @@
+---
+title: split_list
+tags: 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.
+
+```py
+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)]
+```
+
+```py
+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]]
+```