Kotlin Sequence toList Function

The toList function in Kotlin is used to convert a sequence into a list. It is part of the Kotlin standard library and allows you to create a list from the elements of a sequence, providing a convenient way to collect the results of sequence operations.

Table of Contents

1. Introduction
2. toList Function Syntax
3. Understanding toList
4. Examples
   • Basic Usage
   • Converting a Sequence of Numbers
   • Using toList with Complex Transformations
   • Chaining toList with Other Functions
5. Real-World Use Case
6. Conclusion

Introduction

The toList function allows you to convert a sequence into a list. This is useful for scenarios where you want to collect the results of sequence operations into a list, enabling further manipulation and processing of the data in a familiar list format.

toList Function Syntax

The syntax for the toList function is as follows:

fun <T> Sequence<T>.toList(): List<T>

Returns:

• A new list containing all the elements of the sequence.

Understanding toList

The toList function takes a sequence and collects its elements into a list. This operation is terminal, meaning it triggers the evaluation of the sequence and produces a concrete collection containing the elements.

Examples

Basic Usage

To demonstrate the basic usage of toList, we will create a sequence and convert it to a list.

Example

fun main() {
    val numbers = sequenceOf(1, 2, 3, 4, 5)
    val numberList = numbers.toList()
    println(numberList) // Output: [1, 2, 3, 4, 5]
}

Output:

[1, 2, 3, 4, 5]

Converting a Sequence of Numbers

This example shows how to convert a sequence of numbers into a list.

Example

fun main() {
    val evenNumbers = generateSequence(2) { it + 2 }.take(5)
    val evenNumberList = evenNumbers.toList()
    println(evenNumberList) // Output: [2, 4, 6, 8, 10]
}

Output:

[2, 4, 6, 8, 10]

Using toList with Complex Transformations

You can use the toList function to collect the results of complex sequence transformations into a list.

Example

fun main() {
    val numbers = sequenceOf(1, 2, 3, 4, 5)
    val transformedList = numbers.map { it * 2 }
                                 .filter { it > 5 }
                                 .toList()
    println(transformedList) // Output: [6, 8, 10]
}

Output:

[6, 8, 10]

Chaining toList with Other Functions

The toList function can be chained with other sequence functions to perform complex operations and collect the results into a list.

Example

fun main() {
    val words = sequenceOf("Kotlin", "is", "fun")
    val resultList = words.flatMap { it.asSequence() }
                          .map { it.toUpperCase() }
                          .toList()
    println(resultList) // Output: [K, O, T, L, I, N, I, S, F, U, N]
}

Output:

[K, O, T, L, I, N, I, S, F, U, N]

Real-World Use Case

Processing and Collecting Data

In real-world applications, the toList function can be used to process and collect data from various sources into a list for further analysis or manipulation.

Example

data class Person(val name: String, val age: Int)

fun main() {
    val people = sequenceOf(
        Person("Alice", 30),
        Person("Bob", 25),
        Person("Charlie", 35)
    )

    val namesList = people.filter { it.age > 30 }
                          .map { it.name }
                          .toList()
    println(namesList) // Output: [Charlie]
}

Output:

[Charlie]

Conclusion

The toList function in Kotlin provides used for converting sequences into lists. By understanding and using the toList function, you can efficiently collect the results of sequence operations into a list, enabling further manipulation and analysis of the data in your Kotlin applications.