extract_values_from_collection

# File actionview/lib/action_view/helpers/form_options_helper.rb, line 794
        def extract_values_from_collection(collection, value_method, selected)
          if selected.is_a?(Proc)
            collection.map do |element|
              element.public_send(value_method) if selected.call(element)
            end.compact
          else
            selected
          end
        end