ZREM for removal in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of removing members with ZREM?

Given a sorted set myzset with members and scores:

ZADD myzset 1 one 2 two 3 three

What will be the output of the command:

ZREM myzset two four

and what will be the new members in myzset?

Redis

ZADD myzset 1 one 2 two 3 three
ZREM myzset two four
ZRANGE myzset 0 -1 WITHSCORES

A Output of ZREM: 0; New members: one (1), two (2), three (3)

B Output of ZREM: 2; New members: one (1), three (3)

C Output of ZREM: 1; New members: one (1), three (3)

D Output of ZREM: 1; New members: one (1), two (2), three (3)

💡 Hint

ZREM returns the number of members actually removed. Only existing members count.

The command ZREM myzset two four tries to remove 'two' and 'four'. 'two' exists and is removed, 'four' does not exist. So the output is 1. The remaining members are 'one' and 'three'.

🧠 Conceptual

intermediate

Understanding ZREM behavior with non-existing members

If you run ZREM myzset a b c on a sorted set myzset that contains only x and y, what will be the output?

A 0

B 3

C Error

D 1

💡 Hint

ZREM counts only members that were actually removed.

Since none of 'a', 'b', or 'c' exist in the set, no members are removed, so the output is 0.

📝 Syntax

advanced

Which ZREM command syntax is correct?

Which of the following commands correctly removes members 'a' and 'b' from the sorted set 'myzset'?

A ZREM myzset a b

B ZREM myzset [a, b]

C ZREM myzset {a, b}

D ZREM myzset 'a b'

💡 Hint

ZREM takes the key followed by one or more members separated by spaces.

The correct syntax is to list members separated by spaces without brackets or quotes. Options A, B, and C are invalid syntax.

❓ optimization

advanced

Efficient removal of multiple members with ZREM

You want to remove 100 members from a sorted set in Redis. Which approach is the most efficient?

A Call ZREM 100 times, each time with one member

B Call ZREM once with all 100 members listed

C Call ZREM twice with 50 members each time

D Call ZREM once with a comma-separated string of members

💡 Hint

Fewer calls to Redis server reduce overhead.

Calling ZREM once with all members reduces network overhead and is more efficient than multiple calls.

🔧 Debug

expert

Why does this ZREM command fail?

You run the command:

ZREM myzset 1 2 3

but it does not remove any members, even though you expect members '1', '2', and '3' to be removed. What is the most likely reason?

A ZREM only removes members with scores matching the arguments

B ZREM requires the scores to be specified along with members

C myzset does not exist

D The members are stored as strings, but you are passing numbers without quotes

💡 Hint

Redis stores members as strings exactly as added.

ZREM removes members by exact string match. If members were added as strings '1', '2', '3', passing numbers without quotes may cause no match.