thenBy

inline fun <T> Comparator<T>.thenBy(crossinline selector: (T) -> Comparable<*>?): Comparator<T>(source)

Creates a comparator comparing values after the primary comparator defined them equal. It uses the function to transform value to a Comparable instance for comparison.

Since Kotlin

1.0

Samples

import kotlin.test.*

fun main() { 
   //sampleStart 
   val list = listOf("aa", "b", "bb", "a")

val lengthComparator = compareBy<String> { it.length }
println(list.sortedWith(lengthComparator)) // [b, a, aa, bb]

val lengthThenString = lengthComparator.thenBy { it }
println(list.sortedWith(lengthThenString)) // [a, b, aa, bb] 
   //sampleEnd
}
xxxxxxxxxx
 
val list = listOf("aa", "b", "bb", "a")
val lengthComparator = compareBy<String> { it.length }
println(list.sortedWith(lengthComparator)) // [b, a, aa, bb]
val lengthThenString = lengthComparator.thenBy { it }
println(list.sortedWith(lengthThenString)) // [a, b, aa, bb] 
Open in Playground →
Target: JVMRunning on v.2.1.20

inline fun <T, K> Comparator<T>.thenBy(comparator: Comparator<in K>, crossinline selector: (T) -> K): Comparator<T>(source)

Creates a comparator comparing values after the primary comparator defined them equal. It uses the selector function to transform values and then compares them with the given comparator.

Since Kotlin

1.0

Samples

import kotlin.test.*

fun main() { 
   //sampleStart 
   val list = listOf("A", "aa", "b", "bb", "a")

val lengthComparator = compareBy<String> { it.length }
println(list.sortedWith(lengthComparator)) // [A, b, a, aa, bb]

val lengthThenCaseInsensitive = lengthComparator
    .thenBy(String.CASE_INSENSITIVE_ORDER) { it }
println(list.sortedWith(lengthThenCaseInsensitive)) // [A, a, b, aa, bb] 
   //sampleEnd
}
xxxxxxxxxx
 
val list = listOf("A", "aa", "b", "bb", "a")
val lengthComparator = compareBy<String> { it.length }
println(list.sortedWith(lengthComparator)) // [A, b, a, aa, bb]
val lengthThenCaseInsensitive = lengthComparator
    .thenBy(String.CASE_INSENSITIVE_ORDER) { it }
println(list.sortedWith(lengthThenCaseInsensitive)) // [A, a, b, aa, bb] 
Open in Playground →
Target: JVMRunning on v.2.1.20

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