ZRANK and ZREVRANK for position in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the rank of member 'alice' in the sorted set 'players'.

Redis

ZRANK players [1]

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

Acharlie

Bbob

Calice

Ddave

Attempts:

3 left

💡 Hint

Common Mistakes

Using a member name that does not exist in the sorted set.

Confusing the sorted set name with the member name.

The ZRANK command returns the rank of the specified member in the sorted set. Here, we want the rank of 'alice'.

2fill in blank

medium

Complete the code to get the reverse rank of member 'bob' in the sorted set 'scores'.

Redis

ZREVRANK scores [1]

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

Abob

Balice

Ccharlie

Ddave

Attempts:

3 left

💡 Hint

Common Mistakes

Using ZRANK instead of ZREVRANK for reverse rank.

Using a member name not present in the sorted set.

The ZREVRANK command returns the rank of the member when the sorted set is ordered from highest to lowest score. Here, we want the reverse rank of 'bob'.

3fill in blank

hard

Fix the error in the code to get the rank of 'charlie' in the sorted set 'leaderboard'.

Redis

ZRANK [1] charlie

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

Aplayers

Bleaderboard

Cscores

Dranking

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong sorted set name.

Swapping the member and sorted set arguments.

The first argument to ZRANK is the sorted set name. Here, it should be 'leaderboard' to match the intended sorted set.

4fill in blank

hard

Fill both blanks to get the reverse rank of 'dave' in the sorted set 'game_scores'.

Redis

ZREVRANK [1] [2]

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

Agame_scores

Bdave

Calice

Dplayers

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of sorted set and member.

Using a member not in the sorted set.

The command ZREVRANK requires the sorted set name first, then the member name. Here, 'game_scores' is the sorted set and 'dave' is the member.

5fill in blank

hard

Fill all three blanks to get the rank of 'eve' in the sorted set 'highscores' and then get the reverse rank of 'frank' in the same set.

Redis

ZRANK [1] [2]
ZREVRANK [3] frank

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

Ahighscores

Beve

Dscores

Attempts:

3 left

💡 Hint

Common Mistakes

Using different sorted set names in the two commands.

Mixing up member names.

Both commands use the sorted set name 'highscores'. The first command finds the rank of 'eve', the second finds the reverse rank of 'frank'.

Practice

1. What does the Redis command ZRANK return when used on a sorted set?

easy

A. The total number of members in the sorted set

B. The zero-based rank of a member with scores in ascending order

C. The score of the member in the sorted set

D. The member with the highest score

Solution

1. Step 1: Understand what ZRANK does

   ZRANK returns the position of a member in a sorted set ordered by score from lowest to highest.

2. Step 2: Identify the rank type

   The rank is zero-based, meaning the lowest score member has rank 0.

3. Final Answer:

   The zero-based rank of a member with scores in ascending order -> Option B

4. Quick Check:

   ZRANK = ascending zero-based rank [OK]

Hint: ZRANK ranks ascending, starting at zero [OK]

Common Mistakes:

• Confusing rank with score
• Thinking rank starts at 1
• Mixing ZRANK with ZREVRANK

2. Which of the following is the correct syntax to get the rank of member 'user1' in sorted set 'scores' using ZREVRANK?

easy

A. ZRANK user1 scores

B. ZREVRANK user1 scores

C. ZRANK scores user1

D. ZREVRANK scores user1

Solution

1. Step 1: Recall ZREVRANK command syntax

   The syntax is: ZREVRANK key member

2. Step 2: Apply to given example

   Here, key is 'scores' and member is 'user1', so command is ZREVRANK scores user1

3. Final Answer:

   ZREVRANK scores user1 -> Option D

4. Quick Check:

   ZREVRANK key member syntax [OK]

Hint: Command syntax: ZREVRANK key member [OK]

Common Mistakes:

• Swapping key and member order
• Using ZRANK instead of ZREVRANK
• Adding extra parameters

3. Given a sorted set 'players' with members and scores: {"alice": 50, "bob": 70, "carol": 60}, what is the result of ZRANK players bob?

medium

A. 2

B. 1

C. 0

D. None (member not found)

Solution

1. Step 1: Sort members by ascending score

   Sorted by score ascending: alice(50), carol(60), bob(70)

2. Step 2: Find zero-based rank of 'bob'

   bob is third in order, so rank is 2 (0-based)

3. Final Answer:

   2 -> Option A

4. Quick Check:

   ZRANK ascending order rank = 2 [OK]

Hint: ZRANK counts from lowest score, zero-based [OK]

Common Mistakes:

• Assuming rank is score
• Confusing ascending with descending order
• Using ZREVRANK result instead

4. You run ZREVRANK leaderboard "playerX" but get a null reply. What is the most likely reason?

medium

A. "playerX" is not a member of the sorted set "leaderboard"

B. The command syntax is incorrect

C. The sorted set "leaderboard" is empty

D. ZREVRANK only works on lists, not sorted sets

Solution

1. Step 1: Understand ZREVRANK null reply meaning

   Null reply means the member does not exist in the sorted set.

2. Step 2: Check other options

   Syntax is correct, empty set would also return null but question implies member missing, and ZREVRANK works only on sorted sets.

3. Final Answer:

   "playerX" is not a member of the sorted set "leaderboard" -> Option A

4. Quick Check:

   Null reply means member missing [OK]

Hint: Null reply means member not in set [OK]

Common Mistakes:

• Thinking syntax error causes null
• Assuming empty set returns error
• Confusing data types for ZREVRANK

5. You have a sorted set 'scores' with members and scores: {"x": 10, "y": 20, "z": 30}. You want to find the rank of member 'y' counting from highest score first. Which command and expected result is correct?

hard

A. ZRANK scores y returns 1

B. ZREVRANK scores y returns 2

C. ZREVRANK scores y returns 1

D. ZRANK scores y returns 2

Solution

1. Step 1: Understand ZREVRANK ranks descending

   ZREVRANK ranks members from highest to lowest score, zero-based.

2. Step 2: Sort members descending and find 'y' rank

   Descending order: z(30), y(20), x(10). 'y' is second, so rank is 1.

3. Final Answer:

   ZREVRANK scores y returns 1 -> Option C

4. Quick Check:

   ZREVRANK descending zero-based rank = 1 [OK]

Hint: ZREVRANK ranks from highest score, zero-based [OK]

Common Mistakes:

• Mixing ZRANK and ZREVRANK results
• Counting rank starting at 1 instead of 0
• Confusing ascending and descending order