ZREM for removal in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to remove a member from a sorted set named 'myzset'.

Redis

ZREM myzset [1]

Drag options to blanks, or click blank then click option'

AZADD

Bmyzset

Cmember1

DSREM

Attempts:

3 left

💡 Hint

Common Mistakes

Using the sorted set name instead of the member name.

Using commands like ZADD or SREM instead of the member name.

The ZREM command removes the specified member from the sorted set. Here, member1 is the member to remove.

2fill in blank

medium

Complete the code to remove the member 'user42' from the sorted set 'users'.

Redis

ZREM users [1]

Drag options to blanks, or click blank then click option'

Auser42

Buser24

Cusers

DZADD

Attempts:

3 left

💡 Hint

Common Mistakes

Removing a different member than intended.

Using the sorted set name as the member.

The ZREM command removes the member user42 from the sorted set users.

3fill in blank

hard

Fix the error in the command to remove 'item5' from 'inventory'.

Redis

ZREM [1] item5

Drag options to blanks, or click blank then click option'

ASREM

Bitem5

CZADD

Dinventory

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the member name where the set name should be.

Using other commands like ZADD or SREM.

The first argument after ZREM must be the sorted set name, here inventory. The member to remove is item5.

4fill in blank

hard

Fill both blanks to remove 'alpha' from the sorted set 'letters'.

Redis

ZREM [1] [2]

Drag options to blanks, or click blank then click option'

Aletters

Balpha

Cbeta

Dgamma

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the set name and member names.

Using a member name as the set name.

The first blank is the sorted set name letters. The second blank is the member alpha to remove. To remove multiple members, you can list them all after the set name.

5fill in blank

hard

Fill all three blanks to remove 'red' and 'green' from the sorted set 'colors'.

Redis

ZREM [1] [2] [3]

Drag options to blanks, or click blank then click option'

Acolors

Bred

Cgreen

Dblue

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of set name and members.

Leaving out some members to remove.

The first blank is the sorted set name colors. The next blanks are the members red and green to remove. You can remove multiple members by listing them all after the set name.

Practice

1. What does the Redis command ZREM do?

easy

A. Removes specified members from a sorted set

B. Adds new members to a sorted set

C. Returns the score of a member in a sorted set

D. Deletes the entire sorted set

Solution

1. Step 1: Understand the purpose of ZREM

   The command ZREM is used to remove one or more members from a sorted set in Redis.

2. Step 2: Compare with other commands

   Adding members is done by ZADD, getting scores by ZSCORE, and deleting the whole set by DEL, so these are not correct.

3. Final Answer:

   Removes specified members from a sorted set -> Option A

4. Quick Check:

   ZREM removes members = B [OK]

Hint: ZREM always removes members from sorted sets [OK]

Common Mistakes:

• Confusing ZREM with ZADD
• Thinking ZREM deletes the whole set
• Assuming ZREM returns member scores

2. Which of the following is the correct syntax to remove members 'a' and 'b' from a sorted set named 'myzset' using ZREM?

easy

A. ZREM myzset (a,b)

B. ZREM myzset {a,b}

C. ZREM myzset ['a','b']

D. ZREM myzset a b

Solution

1. Step 1: Recall ZREM syntax

   ZREM command syntax is: ZREM key member [member ...]. Members are listed separated by spaces.

2. Step 2: Analyze options

   ZREM myzset a b uses space-separated members correctly. Options B, C, and D use invalid syntax with braces, brackets, or parentheses which Redis does not accept.

3. Final Answer:

   ZREM myzset a b -> Option D

4. Quick Check:

   Correct ZREM syntax = A [OK]

Hint: List members separated by spaces after key in ZREM [OK]

Common Mistakes:

• Using brackets or braces around members
• Separating members with commas
• Passing members as a single string

3. Given a sorted set 'myzset' with members and scores: {"a":1, "b":2, "c":3}, what will be the result of ZREM myzset b d followed by ZCARD myzset?

medium

A. 1

B. 2

C. 3

D. 0

Solution

1. Step 1: Understand ZREM effect

   ZREM removes specified members if they exist. 'b' exists and will be removed. 'd' does not exist and is ignored without error.

2. Step 2: Calculate remaining members

   Initially 3 members: a, b, c. After removal of 'b', members left are 'a' and 'c', so 2 remain.

3. Final Answer:

   2 -> Option B

4. Quick Check:

   Removed 1 member, 2 remain = C [OK]

Hint: ZREM ignores missing members, count remaining with ZCARD [OK]

Common Mistakes:

• Assuming error on removing non-existent member
• Counting removed non-existent member
• Confusing ZREM with ZADD effect

4. You run the command ZREM myzset without specifying any members. What will happen?

medium

A. Syntax error due to missing members

B. Returns 0 and does nothing

C. Removes the first member by default

D. Removes all members from 'myzset'

Solution

1. Step 1: Check ZREM command requirements

   ZREM requires at least one member argument to remove. Omitting members is invalid syntax.

2. Step 2: Result of missing members

   Running ZREM without members causes a syntax error, Redis will not execute the command.

3. Final Answer:

   Syntax error due to missing members -> Option A

4. Quick Check:

   ZREM needs members, missing causes syntax error = D [OK]

Hint: Always specify members to remove with ZREM [OK]

Common Mistakes:

• Assuming ZREM clears entire set without members
• Expecting default removal of first member
• Thinking it returns 0 silently

5. You have a sorted set 'myzset' with members: {"x":10, "y":20, "z":30}. You want to remove all members with scores less than 25 using ZREM. Which approach correctly achieves this?

hard

A. Use ZREM myzset x y

B. Use ZREM myzset with a score range argument

C. Use ZREMRANGEBYSCORE myzset -inf 24

D. Use ZREM myzset z

Solution

1. Step 1: Understand ZREM limitations

   ZREM removes specified members by name, it cannot remove by score range directly.

2. Step 2: Identify members to remove

   Members x (score 10) and y (score 20) are less than 25, so to remove them by score range, use ZREMRANGEBYSCORE myzset -inf 24.

3. Step 3: Analyze options

   A correctly uses ZREMRANGEBYSCORE to remove by score range. B is invalid syntax. C removes members by name but requires manual identification. D removes wrong member.

4. Final Answer:

   Use ZREMRANGEBYSCORE myzset -inf 24 -> Option C

5. Quick Check:

   Removing by score range requires ZREMRANGEBYSCORE = A [OK]

Hint: Use ZREMRANGEBYSCORE to remove members by score range [OK]

Common Mistakes:

• Trying to remove by score with ZREM
• Using invalid syntax with ZREM
• Removing wrong members by name