# From: http://www.ruby-forum.com/topic/135807
# Author: Nobuyoshi Nakada

class Hash
   def collate(h)
      raise ArgumentError unless h.is_a?(Hash)
      update(h) { |key, *values| values }
      #update(h) { |key, *values| values.flatten.uniq }
   end
end

h1 = {:a=>1, :b=>2 }
h2 = {:a=>3, :b=>4, :c=>5}
h1.collate(h2)
p h1, h2     
#=> {:b=>[2, 4], :a=>[1, 3], :c=>5}
#=> {:b=>4, :a=>3, :c=>5}

puts
h1 = {:a=>1, :b=>2 }
h2 = {:a=>3, :b=>4, :c=>5}
h2.collate(h1)
p h1, h2     
#=> {:b=>2, :a=>1}
#=> {:b=>[4, 2], :a=>[3, 1], :c=>5}