Answer by sazzad for How do I find the index of the first occurrence of a score in a sorted Redis set?

You can use ZCOUNT from negative infinity to your specific score to find the index.

For example, in following sorted set:

> ZADD dewey 1 first 3 second 8 third 21 fourth 55 fifth
(integer) 5

To find the index of 21 (the fourth number):

> ZCOUNT dewey -inf (21
3

Just keep in mind that this is 0-based index.