Elixir filter map entries by a conditional

Question

I have a Map in Elixir which maps from string keys to a value which is a list of attributes. How can I remove the items which do not meet the criteria as I enumerate through the Map?

The map looks like this:

%{"A" => [needed: true], "B" => [needed: false]}

In this case I would check each key/value pair and only keep the ones with needed: true

I have tried doing different combinations of using Enum.map and Enum.each so far.

Answer 1

When you need to filter values out of an enumerable like a Map, Enum.filter/2 is your friend. The trick is that you need to sort of "reassemble" the result back into a map.

%{"A" => [needed: true], "B" => [needed: false]}
|> Enum.filter(fn {_, v} -> Keyword.get(v, :needed) end)
|> Enum.into(%{})

# Result:
%{"A" => [needed: true]}