Redis: How to intersect a "normal" set with a sorted set?

Question

Assume I have a set (or sorted set or list if that would be better) A of 100 to 1000 strings.

Then I have a sorted set B of many more strings, say one million.

Now C should be the intersection of A and B (of the strings of course).

I want to have every tuple (X, SCORE_OF_X_IN_B) where X is in C.

Any Idea?

I got two ideas:

1. Interstore
   • store A a sorted set with every score being 0
   • interstore to D
   • get every item of D
   • delete D
2. Simple loop in client
   • loop over A in my client programm
   • get zscore for every string

While 1. has way too much overhead on the redis side (Has to write for example. The redis page states quite a high time complexity, too http://redis.io/commands/zinterstore), 2. would have |A| database connections and won't be a good choice.

Maybe I could write a redis/lua script which will work like zscore but with an arbitrary number of strings, but I'm not sure if my hoster allows scripts...

So I just wanted to ask SO, if there is an elegant and fast solution available without scripting!

Answer 1

There is a simple solution to your problem: ZINTERSTORE will work with a SET and a ZSET. Try:

redis> sadd foo a (integer) 1 redis> zadd bar 1 a (integer) 1 redis> zadd bar 2 b (integer) 1 redis> zinterstore baz 2 foo bar AGGREGATE MAX (integer) 1 redis> zrange baz 0 -1 withscores 1) "a" 2) "1" 

Edit: I added AGGREGATE MAX above, since redis will give each member of the (non-sorted) set foo a default score of 1, and SUM that with whatever score it has in the (sorted) set bar.