Filtering and Transforming Collections in Kotlin

1. Introduction

• Goal: This tutorial aims to guide you through the process of filtering and transforming collections in Kotlin. We will explore the built-in functions that Kotlin provides to accomplish these tasks.

• What You Will Learn: By the end of this tutorial, you will understand how to filter and transform collections in Kotlin using the filter, map, flatMap, mapNotNull functions, and others.

• Prerequisites: You should have a basic understanding of Kotlin programming, including its syntax and fundamental concepts such as variables, functions, and collections.

2. Step-by-Step Guide

Filtering Collections

Filtering is the process of selecting elements from a collection that satisfy a certain condition. In Kotlin, this is done using the filter function.

val numbers = listOf(1, 2, 3, 4, 5)
val evenNumbers = numbers.filter { it % 2 == 0 }

In this example, it refers to the current element being processed. The code inside the curly braces ({}) is the condition for filtering: in this case, we are selecting only those numbers that are even.

Transforming Collections

Transforming, or mapping, is the process of creating a new collection from an existing one, where each element of the new collection is the result of applying a function to each element of the original collection. This is done using the map function.

val numbers = listOf(1, 2, 3, 4, 5)
val squares = numbers.map { it * it }

In this example, we are creating a new list, squares, where each element is the square of the corresponding element in the original list, numbers.

3. Code Examples

Example 1: Filtering Collection

val numbers = listOf(1, -2, 3, -4, 5)
val positiveNumbers = numbers.filter { it > 0 } // filtering positive numbers
println(positiveNumbers) // Expected output: [1, 3, 5]

Example 2: Mapping Collection

val numbers = listOf(1, 2, 3, 4, 5)
val doubledNumbers = numbers.map { it * 2 } // mapping each number to its double
println(doubledNumbers) // Expected output: [2, 4, 6, 8, 10]

4. Summary

Today, we learned about how to filter and transform collections in Kotlin. We used the filter function to select elements from a collection that satisfy a certain condition, and the map function to create a new collection by applying a function to each element of the original collection.

Next, you can explore more advanced collection processing functions, such as reduce, fold, groupBy, and others. We recommend visiting the Kotlin documentation for more detailed information.

5. Practice Exercises

1. Exercise 1: Given a list of numbers, filter out the odd numbers and map the remaining even numbers to their squares.

Solution:

kotlin val numbers = listOf(1, 2, 3, 4, 5) val result = numbers.filter { it % 2 == 0 }.map { it * it } println(result) // Expected output: [4, 16]

1. Exercise 2: Given a list of strings, create a new list that contains the lengths of each string, but only for strings that start with the letter 'a'.

Solution:

kotlin val words = listOf("apple", "banana", "avocado", "cherry", "apricot") val result = words.filter { it.startsWith("a") }.map { it.length } println(result) // Expected output: [5, 7, 7]

Remember to practice regularly to improve your skills. Happy coding!