Ruby Hash subtract method extended to work for Array and Hash values within the Hash.

Ruby Hash deep subtract

# Examples
#    {:foo => [1,2,3,4]} - {:foo => [1,2]}
#      results in {:foo => [3,4]}
#
#    {:bar => {:baz => [8,9]}, :buz => "deleteme"} - {:bar => 8, :buz => "deleteme"}
#      results in {:bar => {:baz => [9]}, :buz => nil}
#
class Hash
    def - (h)
        self.merge(h) do |k, old, new|
            case old
            when Array then (new.class == Array) ? (old - new) : (old - [new])
            when Hash then (new.class == Hash) ? (old - new) : old
            else (old == new) ? nil : old
            end
        end
    end
end