ZRANK and ZREVRANK for position in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Find the rank of a member using ZRANK

Given a sorted set with members and scores, what is the rank of member 'apple' using ZRANK?

Redis

ZADD fruits 10 apple 20 banana 15 cherry
ZRANK fruits apple

A 1

B 2

C 0

D nil

💡 Hint

ZRANK returns the zero-based rank of the member ordered from lowest to highest score.

The sorted set 'fruits' has 'apple' with score 10, which is the lowest score, so its rank is 0.

❓ query_result

intermediate

Find the reverse rank of a member using ZREVRANK

Given a sorted set with members and scores, what is the reverse rank of member 'banana' using ZREVRANK?

Redis

ZADD fruits 10 apple 20 banana 15 cherry
ZREVRANK fruits banana

A 0

B 1

C 2

D nil

💡 Hint

ZREVRANK returns the zero-based rank of the member ordered from highest to lowest score.

The sorted set 'fruits' has 'banana' with the highest score 20, so its reverse rank is 0.

📝 Syntax

advanced

Identify the error in using ZRANK with a non-existing member

What is the output of the command ZRANK fruits orange if 'orange' is not a member of the sorted set?

Redis

ZADD fruits 10 apple 20 banana 15 cherry
ZRANK fruits orange

A -1

B 0

C Error: member not found

D nil

💡 Hint

ZRANK returns nil if the member does not exist in the sorted set.

Since 'orange' is not in the sorted set, ZRANK returns nil indicating no rank.

❓ query_result

advanced

Compare ZRANK and ZREVRANK outputs

Given the sorted set fruits with scores, what are the outputs of ZRANK fruits cherry and ZREVRANK fruits cherry?

Redis

ZADD fruits 10 apple 20 banana 15 cherry
ZRANK fruits cherry
ZREVRANK fruits cherry

A ZRANK: 1, ZREVRANK: 1

B ZRANK: 2, ZREVRANK: 0

C ZRANK: 1, ZREVRANK: 0

D ZRANK: 0, ZREVRANK: 2

💡 Hint

ZRANK orders from lowest to highest score, ZREVRANK from highest to lowest.

'cherry' has score 15, which is the middle score. So rank is 1 and reverse rank is also 1.

🧠 Conceptual

expert

Understanding rank behavior with duplicate scores

If a sorted set has members with duplicate scores, how does ZRANK determine the rank of a member?

A ZRANK returns the average rank of all members with the same score.

B ZRANK orders members with the same score lexicographically and returns the zero-based rank accordingly.

C ZRANK returns the highest rank among members with the same score.

D ZRANK returns a random rank among members with the same score.

💡 Hint

Redis sorts members with the same score by their member name in alphabetical order.

When scores tie, Redis orders members lexicographically by their member name to assign ranks.