tuple group_by into map

[ndrean]

Suppose you have data in the form [{"M1", "C1"}, {"M1", "C2"}, {"M2", "C3"}] and you want a map "grouped by":
[%{c: ["C2", "C1"], m: "M1"}, %{c: ["C3"], m: "M2"}]

A helper function (perhaps not optimum :)

group_assoc = fn list ->
    list
    |> Enum.map(fn {m, c} -> %{m: m, c: c} end)
    # list_maps = [%{m: "M1", c: "C1"}, %{m: "M1", c: "C2"}, %{m: "M2", c: "C3"}]
    |> Enum.group_by(& &1.m)
    |> Enum.map(fn {k, v} ->
      %{m: k, c: Enum.reduce(v, [], fn e, acc -> [e.c | acc] end)}
    end)
  end