Intersect a SET with a ZSET

Redis‘s SET and ZSET (sorted sets) are a really powerful structure. The only limits are about set operation you can perform. Using Redis you can’t obtain the intersection (or the union) between two sorted set or between a SET and a ZSET. You can use SINTER to intersect a group of SET or SUNION for union. Unfortunately there is no direct way for ZSET.

In our use case, we had to intersect a ZSET (a sorted rank) and a SET (a group of categorized items) to find the rank of the element inside selected category.

After a successful search on Google I found a way on StackOverflow (view below link): use ZINTERSTORE. It’s really simple: act like SINTER but store results into a new ZSET. It has a quite expensive memory footprint but is ok if you frequently reuse the result (is like a cache and you can set expire time using EXPIRE).