gistfile1.rb

module Enumerable
  def group(&block)
    groups = {}
    self.each do |elem|
      the_key = block ? block.call(elem) : elem
      if groups[the_key]
        groups[the_key].push(elem)
      else
        groups[the_key] = [elem]
      end
    end
    return groups.values
  end
end