Elixir meyers_difference for Maps

map_difference.ex

defmodule Boydm.Utilities.Map do

  #============================================================================
  # similar to List.meyers_difference, the below code compares two maps
  # and generates a list of actions that can be applied to the first map
  # to transform it into the second map.

  #--------------------------------------------------------
  def difference(map_1, map_2) when is_map(map_1) and is_map(map_2) do
    # remove any keys from map_1 that are simply not present (at all) in map_2
    difference = Enum.reduce(map_1, [], fn({k,_}, d)->
      case Map.has_key?(map_2, k) do
        false ->  [{:del, k} | d]
        true ->   d
      end
    end)

    # add any puts for keys that have changed between map_2 to map_1
    Enum.reduce(map_2, difference, fn({k,v}, d)->
      case Map.has_key?(map_1, k) && (Map.get(map_1, k) == v) do
        false ->  [{:put, k, v} | d]
        true ->   d
      end
    end)
  end

  #--------------------------------------------------------
  def apply_difference(map, difference) when is_map(map) and is_list(difference) do
    Enum.reduce(difference, map, fn(diff, acc)->
      case diff do
        {:put, k, v} -> Map.put(acc, k, v)
        {:del, k} ->    Map.delete(acc, k)
      end
    end)
  end

end