2018-fumichan-thesis / sinatra-practice / form-sample / vendor / bundle / ruby / 2.5.0 / gems / backports-3.11.4 / lib / backports / 1.8.7 / enumerable / group_by.rb

unless Enumerable.method_defined? :group_by
  require 'enumerator'

  module Enumerable
    def group_by
      return to_enum(:group_by) unless block_given?
      result = {}
      each do |o|
        result.fetch(yield(o)){|key| result[key] = []} << o
      end
      result
    end
  end
end