def keep(key, matcher)
      @items.reject! {|i| (i[key] =~ matcher) ? false : true }
    end
def keep(key, matcher)
      @items.reject! {|i| (i[key] =~ matcher) ? false : true }
    end
Keep items that match the regex

 Usage (block, during initialization):
     Smoke.yql(:ruby) do
       ...
       emit do
         keep(:title, /tuesday/i)
       end
     end
 Keep must be used inside an `emit` block.