ZREVRANK

Introduction and Use Case(s)

The ZREVRANK command in Redis returns the rank of a member in a sorted set, with the scores ordered from high to low. It is particularly useful for reverse ranking scenarios, such as leaderboard systems where you want to know the position of a participant based on their score.

Syntax

  1. ZREVRANK key member

Parameter Explanations

  • key: The name of the sorted set.
  • member: The member whose rank you wish to retrieve.

These parameters are essential for identifying which sorted set and member you are querying.

Return Values

  • Integer: The rank of the member (0-based index).
  • nil: If the member does not exist within the sorted set.

Example Outputs:

  • (integer) 0 when the member is the highest-scoring member.
  • (nil) when the member is not found in the sorted set.

Code Examples

  1. dragonfly> ZADD myzset 1 "one"
  2. (integer) 1
  3. dragonfly> ZADD myzset 2 "two"
  4. (integer) 1
  5. dragonfly> ZADD myzset 3 "three"
  6. (integer) 1
  7. dragonfly> ZREVRANK myzset "one"
  8. (integer) 2
  9. dragonfly> ZREVRANK myzset "three"
  10. (integer) 0
  11. dragonfly> ZREVRANK myzset "four"
  12. (nil)

Best Practices

  • Ensure that the sorted set (key) exists before calling ZREVRANK to avoid unnecessary nil results.
  • Use this command in operations where reverse ranking based on scores is critical, like high-score tables in gaming applications.

Common Mistakes

  • Misinterpreting the 0-based index: A rank of (integer) 0 means the member has the highest score.
  • Forgetting that ZREVRANK returns nil if the member does not exist, which can lead to unhandled exceptions in some applications.

FAQs

Q: What happens if the sorted set does not exist?

A: The command will simply return nil, indicating that the member was not found.

Q: Can ZREVRANK handle negative scores?

A: Yes, ZREVRANK ranks members based on their scores regardless of whether the scores are positive or negative.