Add invert map helper

To be used in UMS

Author: PragTob

lib/together/map.ex

@@ -0,0 +1,28 @@
+defmodule Together.Map do
+  @moduledoc """
+  Helper functions for dealing with maps.
+
+  Would be great to have them in elixir core, but for now they aren't wanted.
+  """
+
+  @doc """
+  Inverts a map, exchanging keys and values.
+
+  ## Examples
+
+      iex> invert(%{a: 1, b: 2})
+      %{1 => :a, 2 => :b}
+
+      # this one depends a bit on ordering of the map inside the BEAM, but wanted to show that
+      # no values get aggregated.
+      iex> invert(%{a: 1, b: 1})
+      %{1 => :b}
+
+      iex> invert(%{})
+      %{}
+  """
+  @spec invert(map) :: map()
+  def invert(map) do
+    Map.new(map, fn {key, value} -> {value, key} end)
+  end
+end

test/together/map_test.exs

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+defmodule Together.MapTest do
+  use ExUnit.Case, async: true
+  doctest Together.Map, import: true
+end