gistfile1.rb

criteria.merge!( :_keywords => { :$in => words } )

search_result = collection.map_reduce(search_map(words), search_reduce, :query => criteria)

      def search_reduce
        "function( key , values ){return values[0];}"
      end

      def search_map(words)
        #convert words into Regex OR
        q = words.map do |k|
          Regexp.escape(k)
        end.join("|")
        "function(){" +
          "this.relevance = this._keywords.filter(" +
          "function(z){" +
          "return String(z).match(/(#{q})/);" +
          "}).length;" +
          "emit(this._id, this);" +
          "}"
      end