`Enum.chunk_by`

I discovered a pretty cool Elixir function this weekend, Enum.chunk_by.

Backstory: I wanted to group a list of strings by equality, while preserving the list order.

Enum.chunk_by takes an enumerable and a function, and breaks that enumerable into an enumerable when the function returns a new or different result.

Here's a simple example:

iex> Enum.chunk_by(['A', 'A', 'A', 'B', 'A'], fn(l) -> l end)
[['A', 'A', 'A'], ['B'], ['A']]

Anytime l changes, a new list is created.

Slightly more complex:

iex> Enum.chunk_by([1, 2, 3, 4, 5], fn(n) -> rem(n, 3) == 0 end)
[[1, 2], [3], [4, 5]]

The function only returns something different (true) on 3, so 3 is assigned to its own list.