Kotlin Sequence sortedByDescending Function

The sortedByDescending function in Kotlin is used to sort the elements in a sequence based on a specified selector function in descending order. It is part of the Kotlin standard library and allows you to sort elements according to custom criteria in reverse order.

Table of Contents

1. Introduction
2. sortedByDescending Function Syntax
3. Understanding sortedByDescending
4. Examples
   • Basic Usage
   • Sorting Strings by Length in Descending Order
   • Using sortedByDescending with Custom Objects
   • Chaining sortedByDescending with Other Functions
5. Real-World Use Case
6. Conclusion

Introduction

The sortedByDescending function allows you to sort the elements of a sequence based on a custom selector function in descending order. This is useful for scenarios where you need to arrange elements in reverse order according to specific criteria, enabling more precise data manipulation and presentation.

sortedByDescending Function Syntax

The syntax for the sortedByDescending function is as follows:

fun <T, R : Comparable<R>> Sequence<T>.sortedByDescending(selector: (T) -> R?): Sequence<T> 

Parameters:

• selector: A lambda function that defines the criteria for sorting the elements.

Returns:

• A sequence with the elements sorted in descending order based on the specified criteria.

Understanding sortedByDescending

The sortedByDescending function takes a sequence and sorts its elements according to the value returned by the selector function for each element, in descending order. This operation is terminal, meaning it triggers the evaluation of the sequence and produces a sorted sequence.

Examples

Basic Usage

To demonstrate the basic usage of sortedByDescending, we will create a sequence of integers and sort them in descending order by their absolute values.

Example

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

Output:

[-5, 4, -3, 2, -1] 

Sorting Strings by Length in Descending Order

This example shows how to sort a sequence of strings by their length in descending order.

Example

fun main() { val names = sequenceOf("Arjun", "Bhaskar", "Chitra", "Deepak", "Esha") val sortedNames = names.sortedByDescending { it.length } println(sortedNames.toList()) // Output: [Bhaskar, Deepak, Chitra, Arjun, Esha] } 

Output:

[Bhaskar, Deepak, Chitra, Arjun, Esha] 

Using sortedByDescending with Custom Objects

You can use the sortedByDescending function to sort custom objects based on specific properties in descending order.

Example

data class Person(val name: String, val age: Int) fun main() { val people = sequenceOf( Person("Arjun", 25), Person("Bhaskar", 30), Person("Chitra", 22), Person("Deepak", 28), Person("Esha", 26) ) val sortedByAgeDescending = people.sortedByDescending { it.age } println(sortedByAgeDescending.toList()) // Output: [Person(name=Bhaskar, age=30), Person(name=Deepak, age=28), Person(name=Esha, age=26), Person(name=Arjun, age=25), Person(name=Chitra, age=22)] } 

Output:

[Person(name=Bhaskar, age=30), Person(name=Deepak, age=28), Person(name=Esha, age=26), Person(name=Arjun, age=25), Person(name=Chitra, age=22)] 

Chaining sortedByDescending with Other Functions

The sortedByDescending function can be chained with other sequence functions to perform complex operations and sorting.

Example

fun main() { val numbers = sequenceOf(5, 3, 1, 4, 2) val result = numbers.filter { it % 2 == 0 } .sortedByDescending { it } .map { it * 2 } println(result.toList()) // Output: [8, 4] } 

Output:

[8, 4] 

Real-World Use Case

Sorting Products by Price in Descending Order

In real-world applications, the sortedByDescending function can be used to sort products by price, name, or other attributes in descending order.

Example

data class Product(val name: String, val price: Double) fun main() { val products = sequenceOf( Product("Laptop", 999.99), Product("Smartphone", 499.99), Product("Tablet", 299.99), Product("Smartwatch", 199.99) ) val sortedByPriceDescending = products.sortedByDescending { it.price } println(sortedByPriceDescending.toList()) // Output: [Product(name=Laptop, price=999.99), Product(name=Smartphone, price=499.99), Product(name=Tablet, price=299.99), Product(name=Smartwatch, price=199.99)] } 

Output:

[Product(name=Laptop, price=999.99), Product(name=Smartphone, price=499.99), Product(name=Tablet, price=299.99), Product(name=Smartwatch, price=199.99)] 

Conclusion

The sortedByDescending function in Kotlin provides used for sorting elements in a sequence based on custom criteria in descending order. By understanding and using the sortedByDescending function, you can efficiently organize data in your Kotlin applications, making them more flexible and responsive to user needs.