def delete_item(item)
      Predictor.redis.watch(redis_key(:sets, item)) do
        sets = Predictor.redis.smembers(redis_key(:sets, item))
        Predictor.redis.multi do |multi|
          sets.each do |set|
            multi.srem(redis_key(:items, set), item)
          end

          multi.del redis_key(:sets, item)
        end
      end
    end
def delete_item(item)
      Predictor.redis.watch(redis_key(:sets, item)) do
        sets = Predictor.redis.smembers(redis_key(:sets, item))
        Predictor.redis.multi do |multi|
          sets.each do |set|
            multi.srem(redis_key(:items, set), item)
          end

          multi.del redis_key(:sets, item)
        end
      end
    end
delete item from the matrix