Unique visitor tracking with sets in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a visitor ID to the set of unique visitors for today.

Redis

SADD unique_visitors:2024-06-01 [1]

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

Avisitor123

BGET

CDEL

DSET

Attempts:

3 left

💡 Hint

Common Mistakes

Using commands like GET or DEL instead of the visitor ID.

Forgetting to specify the visitor ID.

The SADD command adds a member to a set. Here, we add the visitor ID visitor123 to the set unique_visitors:2024-06-01.

2fill in blank

medium

Complete the code to count how many unique visitors visited today.

Redis

SCARD [1]

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

Avisitors_today

Bvisitor_count

Cunique_visitors:2024-06-01

Dunique_visitors

Attempts:

3 left

💡 Hint

Common Mistakes

Using a key that does not exist or is not a set.

Confusing SCARD with other commands like GET.

The SCARD command returns the number of members in a set. We use the key unique_visitors:2024-06-01 to count today's unique visitors.

3fill in blank

hard

Fix the error in the code to get the union of unique visitors from two days.

Redis

SUNION unique_visitors:2024-06-01 [1]

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

Aunique_visitors:2024-06-01

Bunique_visitors:2024-06-03

Cunique_visitors

Dunique_visitors:2024-06-02

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same key twice.

Using a key that does not exist.

The SUNION command returns the union of sets. To get visitors from two days, use the keys for those days. Here, we fix the second key to unique_visitors:2024-06-02.

4fill in blank

hard

Fill both blanks to store the union of two days' unique visitors into a new set.

Redis

SUNIONSTORE [1] unique_visitors:2024-06-01 [2]

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

Aunique_visitors:2024-06-01-02

Bunique_visitors:2024-06-03

Cunique_visitors:2024-06-02

Dunique_visitors:2024-06-04

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up source and destination keys.

Using keys that do not exist.

SUNIONSTORE saves the union of sets into a new key. We store the union of unique_visitors:2024-06-01 and unique_visitors:2024-06-02 into unique_visitors:2024-06-01-02.

5fill in blank

hard

Fill all three blanks to find the intersection of three days' unique visitors and store it in a new set.

Redis

SINTERSTORE [1] unique_visitors:2024-06-01 [2] [3]

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

Aunique_visitors:2024-06-01-02-03

Bunique_visitors:2024-06-02

Cunique_visitors:2024-06-03

Dunique_visitors:2024-06-04

Attempts:

3 left

💡 Hint

Common Mistakes

Using keys that do not exist.

Confusing intersection with union commands.

SINTERSTORE stores the intersection of sets into a new key. Here, we find visitors common to June 1, 2, and 3, and store them in unique_visitors:2024-06-01-02-03.

Practice

1. What is the main advantage of using Redis sets for unique visitor tracking?

easy

A. They automatically prevent duplicate visitor IDs.

B. They store visitor data in sorted order.

C. They allow storing large text data efficiently.

D. They provide built-in encryption for visitor IDs.

Solution

1. Step 1: Understand Redis sets behavior

   Redis sets store unique elements only, so duplicates are not saved.

2. Step 2: Relate to visitor tracking

   This means each visitor ID is stored once, ensuring uniqueness automatically.

3. Final Answer:

   They automatically prevent duplicate visitor IDs. -> Option A

4. Quick Check:

   Redis sets = unique elements [OK]

Hint: Remember: sets never store duplicates [OK]

Common Mistakes:

• Thinking sets store elements in order
• Confusing sets with lists or hashes
• Assuming sets encrypt data automatically

2. Which Redis command correctly adds a visitor ID 'user123' to a set named 'visitors'?

easy

A. SET visitors user123

B. ADD visitors user123

C. SADD visitors user123

D. APPEND visitors user123

Solution

1. Step 1: Identify the correct command to add to a set

   The Redis command to add members to a set is SADD.

2. Step 2: Check syntax correctness

   SADD visitors user123 adds 'user123' to the 'visitors' set correctly.

3. Final Answer:

   SADD visitors user123 -> Option C

4. Quick Check:

   SADD adds members to sets [OK]

Hint: Use SADD to add members to sets [OK]

Common Mistakes:

• Using SET which is for strings, not sets
• Using ADD which is invalid in Redis
• Using APPEND which is for strings

3. Given the following Redis commands executed in order:

SADD visitors user1
SADD visitors user2
SADD visitors user1
SCARD visitors

What will be the output of SCARD visitors?

medium

A. 2

B. 0

C. 1

D. 3

Solution

1. Step 1: Analyze SADD commands

   First adds 'user1', second adds 'user2', third tries to add 'user1' again (ignored as duplicate).

2. Step 2: Understand SCARD output

   SCARD returns the count of unique members in the set, which are 'user1' and 'user2'.

3. Final Answer:

   2 -> Option A

4. Quick Check:

   Unique visitors count = 2 [OK]

Hint: SCARD counts unique set members [OK]

Common Mistakes:

• Counting duplicates as separate members
• Confusing SCARD with SMEMBERS output
• Assuming SCARD returns all added commands count

4. You run the command SADD visitors without specifying any visitor ID. What will happen?

medium

A. A new empty set is created.

B. An error occurs due to missing member argument.

C. The command adds a null member to the set.

D. The command is ignored silently.

Solution

1. Step 1: Check SADD command requirements

   SADD requires at least one member argument to add to the set.

2. Step 2: Result of missing member argument

   Running SADD without members causes a syntax error in Redis.

3. Final Answer:

   An error occurs due to missing member argument. -> Option B

4. Quick Check:

   SADD needs members, else error [OK]

Hint: SADD must have at least one member argument [OK]

Common Mistakes:

• Assuming empty sets can be created with SADD alone
• Thinking null or empty string is added automatically
• Expecting silent failure without error

5. You want to track unique visitors for multiple days using Redis sets. Which approach correctly counts total unique visitors across days stored as sets 'day1', 'day2', and 'day3'?

hard

A. Use DEL day1 day2 day3 then SCARD total.

B. Use SINTERSTORE total day1 day2 day3 then SCARD total.

C. Use SMEMBERS day1 then count manually.

D. Use SUNIONSTORE total day1 day2 day3 then SCARD total.

Solution

1. Step 1: Understand set operations for unique visitors

   To combine unique visitors from multiple sets, use SUNIONSTORE to create a union set.

2. Step 2: Count unique visitors in combined set

   After union, SCARD on the combined set gives total unique visitors across days.

3. Final Answer:

   Use SUNIONSTORE total day1 day2 day3 then SCARD total. -> Option D

4. Quick Check:

   Union sets + SCARD = total unique visitors [OK]

Hint: Use SUNIONSTORE to combine sets before counting [OK]

Common Mistakes:

• Using SINTERSTORE which finds common visitors only
• Counting members manually instead of using SCARD
• Deleting sets before counting unique visitors