Why collection operations replace loops in Kotlin - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to filter a list of numbers to keep only even numbers.

Kotlin

val evens = numbers.[1] { it % 2 == 0 }

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Afilter

Bmap

Creduce

DforEach

Attempts:

3 left

💡 Hint

Common Mistakes

Using map instead of filter returns transformed elements, not filtered ones.

The filter function selects elements matching the condition.

2fill in blank

medium

Complete the code to transform a list of strings to their lengths.

Kotlin

val lengths = words.[1] { it.length }

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Afilter

BforEach

Cfold

Dmap

Attempts:

3 left

💡 Hint

Common Mistakes

Using filter returns a subset, not transformed elements.

The map function transforms each element to another value.

3fill in blank

hard

Fix the error in the code to sum all numbers in the list.

Kotlin

val total = numbers.[1] { acc, num -> acc + num }

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AforEach

Bmap

Creduce

Dfilter

Attempts:

3 left

💡 Hint

Common Mistakes

Using map returns a list, not a single combined value.

The reduce function combines elements using the lambda to produce a single result.

4fill in blank

hard

Fill both blanks to create a map of words to their uppercase forms, filtering only words longer than 3 letters.

Kotlin

val result = words.[1] { it.length > 3 }.[2] { it to it.uppercase() }

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

Afilter

Bmap

Creduce

DforEach

Attempts:

3 left

💡 Hint

Common Mistakes

Using map before filter changes all elements before filtering.

First, filter keeps words longer than 3 letters, then map transforms each word to a pair of the word and its uppercase.

5fill in blank

hard

Fill all three blanks to create a map of uppercase words to their lengths, filtering words starting with 'a'.

Kotlin

val result = words.[1] { it.startsWith("a") }.[2] { it.uppercase() }.[3] { it to it.length }

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

Afilter

Bmap

Cassociate

Dreduce

Attempts:

3 left

💡 Hint

Common Mistakes

Using reduce instead of associate does not create a map.

First, filter selects words starting with 'a', then map converts them to uppercase, and finally associate creates a map from uppercase words to their lengths.