FlatMap for nested collections in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to flatten the list of lists using flatMap.

Kotlin

val nestedList = listOf(listOf(1, 2), listOf(3, 4))
val flatList = nestedList.[1] { it }
println(flatList)

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

Amap

Bfilter

CflatMap

DforEach

Attempts:

3 left

💡 Hint

Common Mistakes

Using map instead of flatMap results in a list of lists, not a flat list.

The flatMap function flattens the nested lists into a single list by applying the given lambda.

2fill in blank

medium

Complete the code to extract all words from a list of sentences using flatMap.

Kotlin

val sentences = listOf("hello world", "kotlin is fun")
val words = sentences.[1] { it.split(" ") }
println(words)

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

AflatMap

Bmap

Cfilter

Dreduce

Attempts:

3 left

💡 Hint

Common Mistakes

Using map will create a list of lists of words instead of a flat list.

flatMap applies the lambda to each sentence and flattens the resulting lists of words into one list.

3fill in blank

hard

Fix the error in the code to flatten a list of nullable lists using flatMap.

Kotlin

val listOfNullableLists: List<List<Int>?> = listOf(listOf(1, 2), null, listOf(3))
val flatList = listOfNullableLists.[1] { it ?: emptyList() }
println(flatList)

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

Aflatten

BfilterNotNull

Cmap

DflatMap

Attempts:

3 left

💡 Hint

Common Mistakes

Using map will keep the nested structure.

Using flatten directly on nullable lists causes errors.

flatMap is used with a lambda that replaces null with an empty list to safely flatten the collection.

4fill in blank

hard

Fill both blanks to create a flat list of all characters from a list of words.

Kotlin

val words = listOf("cat", "dog")
val chars = words.[1] { it.[2]() }
println(chars)

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

AflatMap

Bmap

CtoList

DtoCharArray

Attempts:

3 left

💡 Hint

Common Mistakes

Using map instead of flatMap results in a list of arrays, not a flat list.

Using toList() returns a list of strings, not characters.

flatMap applies the lambda to each word, and toCharArray() converts each word to a list of characters, which are then flattened into one list.

5fill in blank

hard

Fill all three blanks to create a map of words to their lengths, but only for words longer than 3 characters.

Kotlin

val words = listOf("apple", "bat", "carrot", "dog")
val result = words.[1] { word ->
    if (word.length [2] 3) mapOf(word [3] word.length) else emptyMap<String, Int>()
}
println(result)

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

AflatMap

B>

Cto

Dmap

Attempts:

3 left

💡 Hint

Common Mistakes

Using flatMap instead of map changes the structure.

Using '<' instead of '>' changes the filter condition.

Using '=' instead of 'to' causes syntax errors.

map transforms each word, the condition checks if length is greater than 3, and to creates a pair for the map.