Enum.map_every

You're seeing just the function map_every, go back to Enum module for more information.
Link to this function

map_every(enumerable, nth, fun)

View Source (since 1.4.0)

Specs

map_every(t(), non_neg_integer(), (element() -> any())) :: list()

Returns a list of results of invoking fun on every nth element of enumerable, starting with the first element.

The first element is always passed to the given function, unless nth is 0.

The second argument specifying every nth element must be a non-negative integer.

If nth is 0, then enumerable is directly converted to a list, without fun being ever applied.

Examples

iex> Enum.map_every(1..10, 2, fn x -> x + 1000 end)
[1001, 2, 1003, 4, 1005, 6, 1007, 8, 1009, 10]

iex> Enum.map_every(1..10, 3, fn x -> x + 1000 end)
[1001, 2, 3, 1004, 5, 6, 1007, 8, 9, 1010]

iex> Enum.map_every(1..5, 0, fn x -> x + 1000 end)
[1, 2, 3, 4, 5]

iex> Enum.map_every([1, 2, 3], 1, fn x -> x + 1000 end)
[1001, 1002, 1003]