Update a map that is outside scope of an iterator

Questions / Help
, ,
1

For each key in map_A (we don’t care about the values) get another known map (for example sake: map_B ) which is referenced by the key at map_A (that we are looping) and test whether any of the keys in map_B matches some variable x . If match, update value at key in map_A to "yes" , else "no" .

    x = "something"
    map_A = %{"a" => "no", "b" => "no"}

    for f <- Map.keys(map_A) do
        if(Enum.member?(Map.keys(map_B), x) == true) do
            Map.replace(map_A, f, "yes")
        else
            Map.replace(map_A, f, "no")
        end
     end

The problem is that Map.replace(map_A, f, "yes | no") cannot affect map_A outside of the for iteration. The same would apply for Enum.each/2.

2

map_A = Enum.reduce(map_A, %{}, fn {k, v}, out ->
if Enum.member?(Map.keys(map_B), x) == true) do
Map.put(out, k, “yes”)
else
Map.put(out, k, “no”)
end
end)

You need to remember that whatever way you do it you need to assign the output of the function to your variable.

3

This is what I’ve got from the code you provided. I pulled out the calculation of the value, because it wasn’t depending on any of the values in map_A, so there’s no reason to repeat that logic.

x = "something"
map_A = %{"a" => "no", "b" => "no"}
value =
  map_B
  |> Map.keys()
  |> Enum.member?(x)
  |> if(do: "yes", else: "no")
  
Map.new(map_A, fn {key, _} -> {key, value} end)