Map transformation in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new map with values doubled.

Kotlin

val numbers = mapOf("a" to 1, "b" to 2, "c" to 3)
val doubled = numbers.mapValues { it.value [1] 2 }
println(doubled)

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

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' adds 2 instead of doubling.

Using '-' or '/' changes values incorrectly.

We use * to multiply each value by 2 to double it.

2fill in blank

medium

Complete the code to filter map entries with values greater than 2.

Kotlin

val numbers = mapOf("a" to 1, "b" to 3, "c" to 4)
val filtered = numbers.filter { it.value [1] 2 }
println(filtered)

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

A<

B<=

C==

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' filters smaller values.

Using '==' filters only values equal to 2.

We use '>' to keep entries with values greater than 2.

3fill in blank

hard

Fix the error in the code to convert map keys to uppercase.

Kotlin

val original = mapOf("one" to 1, "two" to 2)
val upperKeys = original.mapKeys { it.key.[1]() }
println(upperKeys)

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

AtoLowerCase

Buppercase

CtoUpperCase

Dcapitalize

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'toUpperCase()' is deprecated in modern Kotlin.

Using 'toLowerCase()' changes to lowercase, not uppercase.

In Kotlin 1.5+, 'uppercase()' is the correct function to convert strings to uppercase.

4fill in blank

hard

Fill both blanks to create a map of word lengths for words longer than 3 letters.

Kotlin

val words = listOf("cat", "house", "tree", "a")
val lengths = words.filter { it.length [1] 3 }.associateWith { it.[2] }
println(lengths)

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

A>

Blength

C<

Dfirst

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' filters shorter words.

Using 'first' returns first character, not length.

We filter words with length > 3 and map each word to its length.

5fill in blank

hard

Fill all three blanks to create a map with uppercase keys and values doubled for values > 1.

Kotlin

val data = mapOf("x" to 1, "y" to 2, "z" to 3)
val result = data.filter { it.value [1] 1 }.mapKeys { it.key.[2]() }.mapValues { it.value [3] 2 }
println(result)

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

A<

B>

C*

Duppercase

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' filters smaller values.

Using 'toUpperCase()' instead of 'uppercase()' in modern Kotlin.

We filter values > 1, convert keys to uppercase, and double the values.

Practice

1. What does the map function do when applied to a list in Kotlin?

easy

A. It removes elements from the list based on a condition.

B. It creates a new list by applying a transformation to each element.

C. It sorts the list in ascending order.

D. It changes the original list by modifying its elements.

Solution

1. Step 1: Understand the purpose of map

   The map function applies a given transformation to each element of the list.

2. Step 2: Check the effect on the list

   It returns a new list with transformed elements without changing the original list.

3. Final Answer:

   It creates a new list by applying a transformation to each element. -> Option B

4. Quick Check:

   map transforms each item and returns new list [OK]

Hint: Remember: map returns a new list, original stays same [OK]

Common Mistakes:

• Thinking map modifies the original list
• Confusing map with filter or sort
• Assuming map removes elements

2. Which of the following is the correct syntax to transform a list of integers by doubling each value using map in Kotlin?

easy

A. val result = list.map { it * 2 }

B. val result = list.map(it * 2)

C. val result = list.map -> it * 2

D. val result = list.map { it + 2 }

Solution

1. Step 1: Identify correct lambda syntax

   The map function requires a lambda inside curly braces: { it * 2 }.

2. Step 2: Check the transformation logic

   Doubling means multiplying by 2, so it * 2 is correct.

3. Final Answer:

   val result = list.map { it * 2 } -> Option A

4. Quick Check:

   Correct lambda syntax with doubling [OK]

Hint: Use curly braces and 'it' for lambda in map [OK]

Common Mistakes:

• Missing curly braces around lambda
• Using parentheses instead of braces
• Wrong operation inside lambda

3. What is the output of the following Kotlin code?

val numbers = listOf(1, 2, 3)
val result = numbers.map { it + 5 }
println(result)

medium

A. [6, 7, 8]

B. [1, 2, 3, 5]

C. [5, 6, 7]

D. [1, 2, 3]

Solution

1. Step 1: Apply the map transformation

   Each element in numbers is increased by 5: 1+5=6, 2+5=7, 3+5=8.

2. Step 2: Form the new list

   The new list is [6, 7, 8], which is printed.

3. Final Answer:

   [6, 7, 8] -> Option A

4. Quick Check:

   Each number +5 = [6, 7, 8] [OK]

Hint: Add 5 to each element inside map to get output [OK]

Common Mistakes:

• Confusing original list with transformed list
• Adding 5 only once instead of to each element
• Misreading the output format

4. Identify the error in this Kotlin code snippet:

val list = listOf(1, 2, 3)
val newList = list.map(it * 3)
println(newList)

medium

A. The multiplication operator is incorrect.

B. Using map on a list is not allowed.

C. The list should be mutable to use map.

D. Missing curly braces around the lambda expression.

Solution

1. Step 1: Check lambda syntax in map

   The map function requires a lambda inside curly braces, but here parentheses are used without braces.

2. Step 2: Confirm correct usage

   Correct syntax is list.map { it * 3 } to apply multiplication.

3. Final Answer:

   Missing curly braces around the lambda expression. -> Option D

4. Quick Check:

   Lambda needs braces in map [OK]

Hint: Always use curly braces for lambda in map [OK]

Common Mistakes:

• Using parentheses instead of braces for lambda
• Thinking map needs mutable list
• Misunderstanding operator usage

5. Given a list of strings val words = listOf("apple", "banana", "cherry"), how can you create a map where each word is a key and its length is the value using Kotlin's map transformation?

hard

A. val wordLengths = words.associateWith { it.length }

B. val wordLengths = words.map { it.length to it }

C. val wordLengths = words.map { it to it.length } .toMap()

D. val wordLengths = words.map { it.length }

Solution

1. Step 1: Understand the goal

   We want a map where keys are words and values are their lengths.

2. Step 2: Use map to create pairs and convert to map

   words.map { it to it.length } creates pairs (word, length). Then toMap() converts the list of pairs to a map.

3. Final Answer:

   val wordLengths = words.map { it to it.length } .toMap() -> Option C

4. Quick Check:

   Map pairs then convert to map [OK]

Hint: Use map to pairs and then toMap() for map creation [OK]

Common Mistakes:

• Using associateWith is correct but not the asked map transformation
• Mapping only lengths returns list, not map
• Swapping key and value in pairs