Enum.group_by

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Link to this function

group_by(enumerable, key_fun, value_fun \\ fn x -> x end)

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Specs

group_by(t(), (element() -> any()), (element() -> any())) :: map()

Splits the enumerable into groups based on key_fun.

The result is a map where each key is given by key_fun and each value is a list of elements given by value_fun. The order of elements within each list is preserved from the enumerable. However, like all maps, the resulting map is unordered.

Examples

iex> Enum.group_by(~w{ant buffalo cat dingo}, &String.length/1)
%{3 => ["ant", "cat"], 5 => ["dingo"], 7 => ["buffalo"]}

iex> Enum.group_by(~w{ant buffalo cat dingo}, &String.length/1, &String.first/1)
%{3 => ["a", "c"], 5 => ["d"], 7 => ["b"]}