Sequence operators (map, filter) in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the map operator do in a Kotlin sequence?

The map operator transforms each element in the sequence by applying a given function, creating a new sequence with the transformed elements.

beginner

What is the purpose of the filter operator in Kotlin sequences?

The filter operator selects elements from the sequence that satisfy a given condition, creating a new sequence with only those elements.

intermediate

How does Kotlin's Sequence differ from a regular List when using map and filter?

A Sequence processes elements lazily, meaning operations like map and filter are applied only when needed, improving performance for large data sets compared to eager List operations.

beginner

What will be the output of this Kotlin code?<br>

val numbers = sequenceOf(1, 2, 3, 4, 5)
val result = numbers.filter { it % 2 == 0 }.map { it * 10 }.toList()
println(result)

The output will be [20, 40]. First, filter selects even numbers (2 and 4), then map multiplies each by 10.

intermediate

Why is chaining map and filter on sequences efficient in Kotlin?

Because sequences use lazy evaluation, chaining map and filter does not create intermediate collections. Elements are processed one by one through the chain, saving memory and time.

What does the filter operator do in a Kotlin sequence?

A Selects elements that meet a condition

B Transforms each element using a function

C Sorts the elements

D Removes duplicates

filter keeps only elements that satisfy the given condition.

Which of the following is true about Kotlin sequences?

A They process elements eagerly

B They process elements lazily

C They cannot be chained with <code>map</code> or <code>filter</code>

D They always return a list

Kotlin sequences use lazy evaluation, processing elements only when needed.

What will sequenceOf(1, 2, 3).map { it * 2 }.toList() return?

A [1, 2, 3]

B An error

C [2, 4, 6]

D [1, 4, 9]

The map multiplies each element by 2, resulting in [2, 4, 6].

Why might you prefer sequences over lists for large data sets?

A Sequences process elements lazily, improving performance

B Sequences use more memory

C Sequences are easier to write

D Sequences do not support <code>map</code> or <code>filter</code>

Lazy processing avoids creating intermediate collections, saving memory and time.

What does this code print?<br>

val seq = sequenceOf(1, 2, 3, 4)
val res = seq.filter { it > 2 }.map { it + 1 }.toList()
println(res)

A [3, 4, 5]

B [1, 2]

C [2, 3, 4]

D [4, 5]

Filter keeps 3 and 4, map adds 1 to each, resulting in [4, 5].

Explain how map and filter work together in Kotlin sequences.

Think about how each operator changes the sequence and how they combine.

Describe the benefits of using sequences with map and filter compared to lists.

Consider how sequences handle data differently than lists.