Grouped and Non-Grouped Options for Select

module ActionView
  module Helpers
     module FormOptionsHelper
      def option_groups_from_collection_for_select(collection, group_method, group_label_method, option_key_method, option_value_method, selected_key = nil)
        collection.map do |group|
          next options_for_select([group], selected_key) if value_for_collection(group, group_method).is_a?(String)

          option_tags = options_from_collection_for_select(
            value_for_collection(group, group_method), option_key_method, option_value_method, selected_key)
          content_tag("optgroup", option_tags, label: value_for_collection(group, group_label_method))
        end.join.html_safe
      end
    end
  end
end