29. Collection operations: filter, map, reduce in Kotlin

February 17, 2025

🔍 Collection Operations in Kotlin: Filter, Map, and Reduce

Welcome, Kotlin developers! In modern programming, working with collections efficiently is crucial. Kotlin provides powerful built-in functions for collection manipulation that can significantly simplify your code and improve readability. Today, we'll dive deep into three fundamental collection operations: filter, map, and reduce.

📌 Understanding Collection Operations

Collection operations in Kotlin are functional programming techniques that allow you to transform, filter, and aggregate data with minimal and expressive code. These operations work on various collection types like List, Set, and Array.

🧩 Filter Operation

The filter operation allows you to select elements from a collection based on a specific condition.

val numbers = listOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
val evenNumbers = numbers.filter { it % 2 == 0 }
// Result: [2, 4, 6, 8, 10]

• Creates a new list with elements matching the predicate • Does not modify the original collection • Works lazily with sequences

🔄 Map Operation

The map operation transforms each element of a collection according to a given transformation function.

val names = listOf("Alice", "Bob", "Charlie")
val nameLengths = names.map { it.length }
// Result: [5, 3, 7]

• Creates a new collection with transformed elements • Preserves the original collection's size • Can perform complex transformations

📊 Reduce Operation

The reduce operation combines collection elements to produce a single result.

val numbers = listOf(1, 2, 3, 4, 5)
val sum = numbers.reduce { acc, number -> acc + number }
// Result: 15

• Combines elements sequentially • Requires at least one element in the collection • Throws an exception for empty collections

🚀 Advanced Combination

You can chain these operations for more complex data transformations:

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

val people = listOf(
    Person("Alice", 25),
    Person("Bob", 30),
    Person("Charlie", 22)
)

val averageAgeOfAdults = people
    .filter { it.age >= 18 }
    .map { it.age }
    .average()
// Result: 25.66

🏋️ Practice Exercises

Create a function that filters strings longer than 5 characters
Transform a list of temperatures from Celsius to Fahrenheit
Calculate the total price of products after applying a discount
Find the longest word in a sentence
Group numbers by their divisibility

Pro Tip: Use sequences for large collections to improve performance and memory efficiency.

🎓 Key Takeaways

Filter selects elements based on a condition
Map transforms collection elements
Reduce combines elements into a single value
These operations are powerful and expressive
They promote functional programming paradigms

🌟 Conclusion

Mastering filter, map, and reduce operations in Kotlin will significantly enhance your programming skills. These functions provide a clean, concise way to manipulate collections and solve complex data processing tasks.

#Kotlin #FunctionalProgramming #CollectionOperations #AndroidDev

📱 Stay Updated with Android Tips!

Join our Telegram channel for exclusive content, useful tips, and the latest Android updates!

👉 Join Our Telegram Channel

Get daily updates and be part of our growing Android community!

android4n00bs