Sorting ArrayList in Kotlin

Question

I have an ArrayList of ArrayList what I want to achieve is, to sort them in descending order (based on the Highest to lowest List size ) to get the largest first and onwards.

I did the same thing in java using Collections. It worked perfectly fine there but now I'm unable to achieve this in Koltin I'm getting an ERROR.

Consider I've a class Foo()

 private var allHistoryList: ArrayList<ArrayList<Foo>> =   arrayListOf()


     /**
                 * Sorting array of array list to get Biggest to smallest array List based of size
                 */

      Collections.sort(allHistoryList, object: Comparator<ArrayList>{
            override fun compare(var a1, var a2) :Int {
                return a2.size() - a1.size()
            }
                    
        }
 

 Collections.sort(allHistoryList, object: Comparator<ArrayList>{
                    override fun compare(var a1 : ArrayList<*>, var a2 :ArrayList<*>) :Int {
                        return a2.size() - a1.size()
                    }
    
                }
    
                )
                //end of sorting

                 /**
                 * Sorting array of array list to get Biggest to smallest array List based of size
                 */
    
 Collections.sort(allHistoryList, new Comparator<ArrayList>() {
                    public int compare(ArrayList a1, ArrayList a2) {
                        return a2.size() - a1.size(); // working fine in Java.
                    }
                });//end of sorting

consider it as Foo for time being.? @GiorgioAntonioli and its not generic List. — Atif AbbAsi
– Atif AbbAsi, Commented Mar 30, 2020 at 8:35

Giorgio Antonioli · Accepted Answer · 2020-03-30 08:44:58Z

13

In Kotlin, it's just one line:

allHistoryList.sortByDescending { list -> list.size }

The method sortByDescending mutates the original list sorting it descending using the size of the list as selector to make the comparison between elements.

answered Mar 30, 2020 at 8:44

Giorgio Antonioli

16.3k10 gold badges52 silver badges73 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Atif AbbAsi · Accepted Answer · 2023-03-05 12:18:11Z

1

import java.util.*

fun main(args: Array<String>) {

    val list = ArrayList<CustomObject>()
    list.add(CustomObject("Z"))
    list.add(CustomObject("A"))
    list.add(CustomObject("B"))
    list.add(CustomObject("X"))
    list.add(CustomObject("Aa"))

    var sortedList = list.sortedWith(compareBy({ it.customProperty }))

    for (obj in sortedList) {
        println(obj.customProperty)
    }
}

edited Mar 5, 2023 at 12:18

Atif AbbAsi

6,0857 gold badges29 silver badges48 bronze badges

answered Jan 5, 2023 at 9:02

aneez ayyappan

113 bronze badges

Collectives™ on Stack Overflow

Sorting ArrayList in Kotlin

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related