keep on trying

hash.rb

class Hash
  def keep_on_trying(*args)
    args.inject(self.dup){|memo, e|  memo.dup.delete(e) if memo.is_a?(Hash)   }
  end
end

ruby-1.9.2-head :109 > a
 => {:test=>{:this=>"aaa"}} 
ruby-1.9.2-head :110 > a.keep_on_trying(:test)
 => {:this=>"aaa"} 
ruby-1.9.2-head :111 > a.keep_on_trying(:test, :this)
 => "aaa" 
ruby-1.9.2-head :112 > a.keep_on_trying(:test, :this, :plz)
 => nil