How do i sort the list of custom objects in kotlin

Last updated Oct 07, 2021


In this kotlin tutorial example we will learn how to sort list of custom objects in kotlin. In the previous example we covered sort mutable list using sort,sorted and sortedDescending methods. To sort the custom object list we will use the following methods

  • sortedBy
  • sortedByDescending
  • sortWith
  • sortedWith

 

So let's create a Custom class Employee which has properties like name and salary.

This Employee class is a data class

data class Employee(var name:String,var salary:Float)

 

Sort custom list using sortedBy

while sort the list using sortedBy method return new list.

import java.util.*

fun main() {

    val employees = listOf(
        Employee("Mallika", 5400f), 
        Employee("Sachin", 30004f),
        Employee("Aish", 12000f),
        Employee("Namitha", 90000f))

    employees.forEach { e-> println("${e.name} ${e.salary}") }

    print("After sort using sortedBy method")
    val sortedEmployee= employees.sortedBy { e->e.salary }
    sortedEmployee.forEach { e-> println("${e.name} ${e.salary}") }

}

data class Employee(var name:String,var salary:Float)

 

Output:

Mallika 5400.0
Sachin 30004.0
Aish 12000.0
Namitha 90000.0
After sort using sortedBy methodMallika 5400.0
Aish 12000.0
Sachin 30004.0
Namitha 90000.0

 

 

Sort list by sortedByDescending

This will sort the given list by descending order based on our constraint

import java.util.*

fun main() {

    val employees = listOf(
        Employee("Mallika", 5400f),
        Employee("Sachin", 30004f),
        Employee("Aish", 12000f),
        Employee("Namitha", 90000f))

    employees.forEach { e-> println("${e.name} ${e.salary}") }

    print("After sort using sortedBy method")
    val sortedEmployee= employees.sortedByDescending { e->e.salary }
    sortedEmployee.forEach { e-> println("${e.name} ${e.salary}") }

}

data class Employee(var name:String,var salary:Float)

 

Output:

Mallika 5400.0
Sachin 30004.0
Aish 12000.0
Namitha 90000.0
After sort using sortedBy methodNamitha 90000.0
Sachin 30004.0
Aish 12000.0
Mallika 5400.0

 

 

Sort list of Custom objects by Compator

Till now we sort the list in ascending or descending order, by using Comparator we will sort the list of custom objects based on our own constraint (conditions).

 

So let's write a program to sort list of custom objects by length of the employee name

import java.util.*

fun main() {

    val employees = listOf(
        Employee("Mallika", 5400f),
        Employee("Sachin", 30004f),
        Employee("Aish", 12000f),
        Employee("Namitha", 90000f))

    employees.forEach { e-> println("${e.name} ${e.salary}") }

    println("After sort using sortedBy method")
    val sortedemployees = employees.sortedWith { student1, student2 -> student1.name.length - student2.name.length }
    sortedemployees.forEach { s -> println(s.name) }

}

data class Employee(var name:String,var salary:Float)

 

Output:

Mallika 5400.0
Sachin 30004.0
Aish 12000.0
Namitha 90000.0
After sort using sortedBy method
Aish
Sachin
Mallika
Namitha

 

 

Sort the list based on Employee salary

import java.util.*

fun main() {

    val employees = listOf(
        Employee("Mallika", 5400f),
        Employee("Sachin", 30004f),
        Employee("Aish", 12000f),
        Employee("Namitha", 90000f))

    employees.forEach { e-> println("${e.name} ${e.salary}") }

    println("After sort using sortedBy method")
    val sortedemployees = employees.sortedWith { student1, student2 -> (student1.salary - student2.salary).toInt() }
    sortedemployees.forEach { s -> println("${s.name} : ${s.salary}") }

}

data class Employee(var name:String,var salary:Float)

 

 

Output:

Mallika 5400.0
Sachin 30004.0
Aish 12000.0
Namitha 90000.0
After sort using sortedBy method
Mallika : 5400.0
Aish : 12000.0
Sachin : 30004.0
Namitha : 90000.0

 

 

Conclusion: In this example we covered sort list of custom objects using sortedBy(),SortedByDescending() and Comparator methods.


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