Set vs sorted set for membership in Redis - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a member exists in a Redis set.

Redis

EXISTS = redis.sismember('myset', [1])

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

A'member1'

B'sortedset'

C'zadd'

D'score'

Attempts:

3 left

💡 Hint

Common Mistakes

Using sorted set commands like ZADD instead of set commands.

Not quoting the member name as a string.

Use sismember with the set name and the member to check membership.

2fill in blank

medium

Complete the code to add a member with a score to a Redis sorted set.

Redis

redis.[1]('myzset', 10, 'member1')

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

Asadd

Bzadd

Czrange

Dsmembers

Attempts:

3 left

💡 Hint

Common Mistakes

Using sadd which does not accept scores.

Using smembers which lists members but does not add.

Use zadd to add a member with a score to a sorted set.

3fill in blank

hard

Fix the error in the code to check membership in a sorted set.

Redis

exists = redis.[1]('myzset', 'member1')

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

Asismember

Bzrem

Czrank

Dzscore

Attempts:

3 left

💡 Hint

Common Mistakes

Using sismember which only works for sets, not sorted sets.

Using zrem which removes members instead of checking.

To check if a member exists in a sorted set, use zscore. It returns the score if the member exists, or None if not.

4fill in blank

hard

Fill both blanks to create a Redis set and add a member.

Redis

redis.[1]('myset')
redis.[2]('myset', 'member1')

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

Adelete

Bsadd

Czadd

Dexists

Attempts:

3 left

💡 Hint

Common Mistakes

Using zadd which is for sorted sets, not sets.

Trying to add members before deleting existing keys.

First, delete any existing set with delete to start fresh, then add a member with sadd.

5fill in blank

hard

Fill all three blanks to check membership in a set and a sorted set.

Redis

is_in_set = redis.[1]('myset', 'member1')
is_in_zset = redis.[2]('myzset', 'member1') is not None
redis.[3]('myzset', 5, 'member2')

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

Asismember

Bzscore

Czadd

Dsmembers

Attempts:

3 left

💡 Hint

Common Mistakes

Using sismember for sorted sets.

Using smembers to check membership instead of sismember.

Use sismember to check membership in a set, zscore to check membership in a sorted set, and zadd to add a member with a score to a sorted set.

Practice

1. Which Redis data structure is best for quickly checking if an item exists without caring about order?

easy

A. Set

B. Sorted Set

C. List

D. Hash

Solution

1. Step 1: Understand the purpose of Sets

   Sets store unique items and allow fast membership checks without any order.

2. Step 2: Compare with Sorted Sets

   Sorted Sets also store unique items but maintain order using scores, which is unnecessary if order doesn't matter.

3. Final Answer:

   Set -> Option A

4. Quick Check:

   Membership without order = Set [OK]

Hint: Use Set for membership checks without order [OK]

Common Mistakes:

• Confusing Sorted Set with Set for membership
• Thinking List is best for membership
• Assuming Hash stores unique items like Set

2. Which Redis command correctly adds a member to a Set named myset?

easy

A. SADD myset member1

B. ZADD myset 1 member1

C. LPUSH myset member1

D. HSET myset member1 1

Solution

1. Step 1: Identify the command for adding to a Set

   The command SADD adds members to a Set in Redis.

2. Step 2: Check other commands

   ZADD is for Sorted Sets, LPUSH is for Lists, and HSET is for Hashes.

3. Final Answer:

   SADD myset member1 -> Option A

4. Quick Check:

   SADD adds to Set [OK]

Hint: Use SADD to add members to a Set [OK]

Common Mistakes:

• Using ZADD for Sets
• Using LPUSH which is for Lists
• Using HSET which is for Hashes

3. Given the commands:
SADD fruits apple banana orange
ZADD scores 10 alice 20 bob 15 carol
Which command checks if 'banana' is a member of the Set fruits?

medium

A. SISMEMBER scores banana

B. ZSCORE fruits banana

C. ZRANK fruits banana

D. SISMEMBER fruits banana

Solution

1. Step 1: Identify the correct membership check for Sets

   SISMEMBER checks if an item is in a Set.

2. Step 2: Match the key and member

   The Set is fruits, and we check for 'banana'. So SISMEMBER fruits banana is correct.

3. Final Answer:

   SISMEMBER fruits banana -> Option D

4. Quick Check:

   Check membership in Set = SISMEMBER [OK]

Hint: Use SISMEMBER for Set membership checks [OK]

Common Mistakes:

• Using ZSCORE or ZRANK on Sets
• Checking membership on wrong key
• Confusing Sorted Set commands with Set commands

4. You want to check if 'alice' is in a Sorted Set scores. Which command is incorrect and will cause an error?

medium

A. ZRANK scores alice

B. ZSCORE scores alice

C. SISMEMBER scores alice

D. ZREM scores alice

Solution

1. Step 1: Understand commands for Sorted Sets

   ZSCORE, ZRANK, and ZREM are valid Sorted Set commands.

2. Step 2: Identify the invalid command

   SISMEMBER is only for Sets, not Sorted Sets, so it will cause an error.

3. Final Answer:

   SISMEMBER scores alice -> Option C

4. Quick Check:

   SISMEMBER invalid for Sorted Set [OK]

Hint: SISMEMBER works only on Sets, not Sorted Sets [OK]

Common Mistakes:

• Using SISMEMBER on Sorted Sets
• Confusing ZREM with SREM
• Assuming SISMEMBER works on all collections

5. You have a leaderboard stored as a Sorted Set leaderboard with player scores. You want to check if a player john exists in the leaderboard and get his rank. Which sequence of commands is correct?

hard

A. ZSCORE leaderboard johnSISMEMBER leaderboard john

B. ZSCORE leaderboard johnZRANK leaderboard john

C. ZRANK leaderboard johnSISMEMBER leaderboard john

D. SISMEMBER leaderboard johnZRANK leaderboard john

Solution

1. Step 1: Check existence and score in Sorted Set

   ZSCORE returns the score if the member exists, otherwise null.

2. Step 2: Get the rank if member exists

   ZRANK returns the rank of the member in the Sorted Set.

3. Step 3: Validate command order

   First check score with ZSCORE, then get rank with ZRANK. Using SISMEMBER is invalid for Sorted Sets.

4. Final Answer:

   ZSCORE leaderboard john
   ZRANK leaderboard john -> Option B

5. Quick Check:

   Use ZSCORE then ZRANK for Sorted Set membership and rank [OK]

Hint: Use ZSCORE then ZRANK for Sorted Set membership and rank [OK]

Common Mistakes:

• Using SISMEMBER on Sorted Sets
• Checking rank before confirming existence
• Mixing Set commands with Sorted Set commands