Sorting Array, List, Custom Object and Dates in Kotlin

 Here is some sorting example in KOTLIN.

Sorting Array using ArrayOf

----------

fun sortedArrayOf() {
    val array1 = arrayOf(44,6,1,9,23,11,5,19,3)
    array1.sort()
    println("Sorted array : ${array1.contentToString()}")
}
//output
/*
Sorted array : [1, 3, 5, 6, 9, 11, 19, 23, 44]
 */

IntArray Sorting

----------

fun sortingByIntArray() {
    val intArray = intArrayOf(4, 3, 2, 1)
    intArray.sort()
    println(intArray.joinToString())
    // output : 1, 2, 3, 4
}

 Sorting Alphabetically String Array

---------

fun sortingByAlphabetically() {
    val stringArray = mutableListOf("ccc", "aab","aaa", "zzz", "bbb")
    val tempSortedList = stringArray.sortedWith(compareBy { it })  //it.first() is for first letter only
    println("Sorted by ascending: $tempSortedList")
    //output: Sorted by ascending: [aaa, aab, bbb, ccc, zzz]
}

Get the first element of String Array

---------

fun getFirstDataOfList() {
    val stringArray = mutableListOf("ccc", "aab","aaa", "zzz", "bbb")
    val firstElement = stringArray.first()
    println("First Element: $firstElement")
    //output : First Element: ccc
}

Sorting Date Ascending

---------

fun sortingByDates() {
    val dates = mutableListOf(
            Date(2020, 3, 8),
            Date(2022, 8, 16),
            Date(2020, 1, 30),
            Date(1999, 1, 5)
    )
//useing sortBy
    dates.sortBy { it.toString() }
    dates.forEach { println(it) }
    println(".........")
//using sortWith
    dates.sortWith(compareBy<Date> { it.year }.thenBy { it.month }.thenBy { it.day })
    dates.forEach { println(it) }
    //for descending: dates.reverse()
    println(".........")
//using sortedWith
    val sortedDates = dates.sortedWith(compareBy<Date> { it.year }.thenBy { it.month }.thenBy { it.day })
    sortedDates.forEach { println(it) }
    //use for descending .reversed()
}

data class Date(val year: Int, val month: Int, val day: Int)

//output
/*  
    Date(year=1999, month=1, day=5)
    Date(year=2020, month=1, day=30)
    Date(year=2020, month=3, day=8)
    Date(year=2022, month=8, day=16)
    .........
    Date(year=1999, month=1, day=5)
    Date(year=2020, month=1, day=30)
    Date(year=2020, month=3, day=8)
    Date(year=2022, month=8, day=16)
    .........
    Date(year=1999, month=1, day=5)
    Date(year=2020, month=1, day=30)
    Date(year=2020, month=3, day=8)
    Date(year=2022, month=8, day=16)
*/

Sorting Ascending array by adding manually 

---------

fun sortByAddingManually() {
    val stringList: MutableList<String> = ArrayList()
    stringList.add("ccc")
    stringList.add("aab")
    stringList.add("aaa")
    stringList.add("zzz")
    stringList.add("bbb")
    stringList.sortBy { it }
    stringList.forEach { println(it) }
}
//output
//aaa
//aab
//bbb
//ccc
//zzz

Sorting by custom object

---------------------------

fun sortedCustomObject() {
    val persons: MutableList<People> = ArrayList()
    persons.add(People("ABC", 61))
    persons.add(People("XZY", 30))
    persons.add(People("ABB",61))
    persons.add(People("XYZ",30))
    persons.add(People("ABZ",61))

    println(".....Sorted Overall Object.....")
    persons.sortBy { it.toString() }
    persons.forEach { println(it) }
    println(".....Sorted First Name and then Age.....")
    val sortedListName = persons.sortedWith(compareBy({ it.name }, { it.age }))
    sortedListName.forEach { println(it) }
    println(".....Sorted First Age and then Name.....")
    val sortedListAge = persons.sortedWith(compareBy({ it.age }, { it.name }))
    sortedListAge.forEach { println(it) }
    println(".....Sorted First Age and then Name...thenBy....")
    persons.sortedWith(compareBy<People> { it.name }.thenBy { it.age })
    persons.forEach { println(it) }
    println(".....using lambda...")
    persons.sortBy { person -> person.age}
    persons.forEach { println(it) }

}
data class People(val name:String, val age: Int)

//output
/*
    .....Sorted Overall Object.....
    People(name=ABB, age=61)
    People(name=ABC, age=61)
    People(name=ABZ, age=60)
    People(name=XYZ, age=30)
    People(name=XZY, age=30)
    .....Sorted First Name and then Age.....
    People(name=ABB, age=61)
    People(name=ABC, age=61)
    People(name=ABZ, age=60)
    People(name=XYZ, age=30)
    People(name=XZY, age=30)
    .....Sorted First Age and then Name.....
    People(name=XYZ, age=30)
    People(name=XZY, age=30)
    People(name=ABZ, age=60)
    People(name=ABB, age=61)
    People(name=ABC, age=61)
*/

More details:

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/sorted.html

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