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ZREVRANK

Introduction​

In Dragonfly, as well as in Redis and Valkey, the ZREVRANK command is used to determine the rank of a member in a sorted set, with the scores ordered from high to low. The rank is counted starting from 0, where 0 is the highest score. This command is useful when you want to rank items such as user scores or product ratings in descending order.

Syntax​

ZREVRANK key member
  • Time complexity: O(log(N))
  • ACL categories: @read, @sortedset, @fast

Parameter Explanations​

  • key: The key of the sorted set.
  • member: The value whose rank you want to retrieve in the sorted set.

Return Values​

  • The command returns the rank of the member in the sorted set, with rank 0 being the highest.
  • If the member does not exist, the command returns nil.

Code Examples​

Basic Example​

Getting the reverse rank of a member in a sorted set:

dragonfly$> ZADD leaderboard 100 "PlayerA" 200 "PlayerB" 150 "PlayerC"
(integer) 3

dragonfly$> ZREVRANK leaderboard "PlayerB"
(integer) 0  # PlayerB has the highest score, so its rank is 0.

Handling Non-Existent Members​

When the specified member is not in the sorted set, ZREVRANK will return nil:

dragonfly$> ZADD leaderboard 100 "PlayerA" 200 "PlayerB" 150 "PlayerC"
(integer) 3

dragonfly$> ZREVRANK leaderboard "PlayerD"
(nil)  # PlayerD does not exist in the sorted set.

Best Practices​

  • Use ZREVRANK when you need to retrieve ranks in descending order of scores. ZREVRANK is particularly useful for leaderboard systems where the highest score appears first.
  • Combine ZREVRANK with ZADD for efficient ranking and scoring of members in real-time ranked systems, such as gaming leaderboards or top-performing products.

Common Mistakes​

  • Assuming the rank is based on ascending order. ZREVRANK specifically orders elements from high to low.
  • Forgetting that if the member does not exist, ZREVRANK will return nil, not an error or zero.

FAQs​

What is the difference between ZREVRANK and ZRANK?​

ZREVRANK gives the rank of the member with scores ordered from highest to lowest, while ZRANK gives the rank from lowest to highest.

What happens if the key does not exist?​

If the key does not exist, ZREVRANK will return nil.