Enumerable#segment

arr = [{:a => 1}, {:a => 2}, {:a => 3}, {:a => 4}, {:b => 3}, {:b => 4}, {:a => 5}]

# I want to get ...
# 
# [
#     {:a => [1,2,3,4]},
#     {:b=> [3,4]},
#     {:a => [5]}
# ]

module Enumerable
  def segment
    self.inject([]) do |memo, curr_obj|
      curr_key = yield(curr_obj)
      prev_key, prev_objs = memo[-1]
      
      if curr_key == prev_key
        prev_objs.push curr_obj
      else
        memo.push [curr_key, [curr_obj]]
      end
      memo
    end
  end
end

puts arr.segment{|h| h.keys.first }.inspect