LINDEX for position access in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the element at index 2 from the list 'mylist'.

Redis

LINDEX mylist [1]

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

A2

B1

C3

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 1 instead of 2, which returns the second element.

Using negative index when positive index is needed.

The LINDEX command retrieves the element at the specified index. Indexing starts at 0, so index 2 is the third element.

2fill in blank

medium

Complete the code to get the last element from the list 'tasks'.

Redis

LINDEX tasks [1]

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

A-1

B0

C1

D-2

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 which returns the first element instead of the last.

Using -2 which returns the second last element.

Using index -1 with LINDEX returns the last element of the list.

3fill in blank

hard

Fix the error in the code to correctly get the first element of the list 'queue'.

Redis

LINDEX queue [1]

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

A1

B2

C-1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 which returns the second element.

Using -1 which returns the last element.

The first element in a Redis list is at index 0. Using any other index will not return the first element.

4fill in blank

hard

Fill both blanks to get the element at index 3 from the list 'events' and the element at index -2 from the list 'logs'.

Redis

LINDEX events [1]
LINDEX logs [2]

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

A3

B-1

C-2

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using -1 instead of -2 for the second last element.

Using 2 instead of 3 for the fourth element.

Index 3 gets the fourth element from 'events'. Index -2 gets the second last element from 'logs'.

5fill in blank

hard

Fill all three blanks to get the first element from 'list1', the last element from 'list2', and the element at index 4 from 'list3'.

Redis

LINDEX list1 [1]
LINDEX list2 [2]
LINDEX list3 [3]

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

A0

B-1

C4

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 instead of 0 for the first element.

Using 0 instead of -1 for the last element.

Using 5 instead of 4 for the fifth element.

Index 0 gets the first element, -1 gets the last element, and 4 gets the fifth element (indexing starts at 0).

Practice

1. What does the Redis command LINDEX mylist 0 do?

easy

A. Deletes the first element of the list 'mylist'.

B. Returns the first element of the list 'mylist'.

C. Returns the length of the list 'mylist'.

D. Adds an element at the start of the list 'mylist'.

Solution

1. Step 1: Understand the LINDEX command

   LINDEX returns the element at the specified index in a Redis list without modifying it.

2. Step 2: Interpret the index 0

   Index 0 means the first element in the list.

3. Final Answer:

   Returns the first element of the list 'mylist'. -> Option B

4. Quick Check:

   LINDEX with 0 returns first element [OK]

Hint: LINDEX with 0 gets first item, -1 gets last [OK]

Common Mistakes:

• Thinking LINDEX deletes or modifies the list
• Confusing LINDEX with LLEN (length)
• Using negative index incorrectly

2. Which of the following is the correct syntax to get the last element of a Redis list named tasks using LINDEX?

easy

A. LINDEX tasks -1

B. LINDEX tasks 1

C. LINDEX tasks 0

D. LINDEX tasks length

Solution

1. Step 1: Recall how to access last element

   In Redis, negative index -1 means the last element in a list.

2. Step 2: Check the options

   Only LINDEX tasks -1 uses -1 correctly to get the last element.

3. Final Answer:

   LINDEX tasks -1 -> Option A

4. Quick Check:

   Negative index -1 returns last element [OK]

Hint: Use -1 index to get last list item with LINDEX [OK]

Common Mistakes:

• Using positive index 1 for last element
• Using 'length' as index (invalid)
• Confusing 0 with last element

3. Given a Redis list colors with elements ["red", "green", "blue", "yellow"], what is the result of LINDEX colors 2?

medium

A. "blue"

B. "yellow"

C. nil

D. "green"

Solution

1. Step 1: Identify list elements and indexes

   List elements: 0:"red", 1:"green", 2:"blue", 3:"yellow".

2. Step 2: Find element at index 2

   Index 2 corresponds to "blue".

3. Final Answer:

   "blue" -> Option A

4. Quick Check:

   Index 2 in list is "blue" [OK]

Hint: Count from 0 to find element at index [OK]

Common Mistakes:

• Counting from 1 instead of 0
• Confusing index 2 with last element
• Expecting nil for valid index

4. You run LINDEX mylist 5 but get (nil) as a result. What is the most likely reason?

medium

A. The index 5 is negative and invalid.

B. LINDEX command is misspelled.

C. The list 'mylist' is empty but has 6 elements.

D. The list 'mylist' has fewer than 6 elements.

Solution

1. Step 1: Understand LINDEX behavior for out-of-range index

   If the index is outside the list range, LINDEX returns nil.

2. Step 2: Analyze index 5

   Index 5 means the 6th element (counting from 0). If list has fewer than 6 elements, result is nil.

3. Final Answer:

   The list 'mylist' has fewer than 6 elements. -> Option D

4. Quick Check:

   Out-of-range index returns nil [OK]

Hint: Index too big returns nil, check list length [OK]

Common Mistakes:

• Assuming nil means syntax error
• Thinking negative index 5 is invalid
• Confusing empty list with list length

5. You have a Redis list fruits with elements ["apple", "banana", "cherry", "date"]. You want to get the second last element using LINDEX. Which command should you use?

hard

A. LINDEX fruits -1

B. LINDEX fruits 2

C. LINDEX fruits -2

D. LINDEX fruits 1

Solution

1. Step 1: Understand negative indexes in LINDEX

   Negative indexes count from the end: -1 is last, -2 is second last.

2. Step 2: Identify second last element index

   Second last element is at index -2.

3. Final Answer:

   LINDEX fruits -2 -> Option C

4. Quick Check:

   Use -2 to get second last element [OK]

Hint: Use -2 index for second last element [OK]

Common Mistakes:

• Using positive index 2 (third element)
• Using -1 which is last element
• Confusing index 1 with second last