Implementing Dense Rank with Redis Sorted Sets

Question

I'm trying to implement a leaderboard with rankings, the data being stored as sorted sets in Redis. The part I'm trying to figure out is how to implement Dense (i.e. "1-2-2-3") ranking, where, for example, users are ranked thusly:

Score   User    Rank
---------------------
22      user1   1
21      user2   2
21      user3   2
21      user4   2
20      user5   3
20      user6   3

This answer: https://stackoverflow.com/a/14944280/2177 is almost what I need, but it amounts to "1-2-2-4" ranking, which is not desirable for my application, e.g.:

1-2-2-4 Ranking 
Score   User    Rank
---------------------
22     user1    1
21     user2    2
21     user3    2
21     user4    2
20     user5    5
20     user6    5

This seems like it would be a fairly common use case. Has anyone successfully implemented such a thing in Redis, and if so, how?

Answer 1

What I ended up doing was adding a second sorted set that contains only the unique scores, which I can then query for their respective positions in the dense ranking.