Subtract Hashes

hashsub.rb

#!/usr/bin/env ruby
require 'pp'

class Hash
  def subtract (h)
    result = {}
    self.each do |k,v|
      result[k] = (self[k] - h[k]) if h[k]
    end
    result
  end
end

h1 = { 'a' => 5,
       'b' => 10,
       'c' => 15 }

h2 = { 'a' => 20,
       'b' => 30,
       'c' => 40 }

pp h2.subtract(h1)

# -> {"a"=>15, "b"=>20, "c"=>25}