Sort a List in Kotlin

Things on this page are fragmentary and immature notes/thoughts of the author. Please read with your own judgement!

sorted¶

If elements in a List implements the Comparable interface, you can call the method sorted to return a sorted List (in nature order).

Note: Pair in Kotin does not implement the Comparable interface!!!

listOf(5, 9, 3, 2).sorted()

[2, 3, 5, 9]

val listPairs = listOf(Pair(5, 7), Pair(5, 3), Pair(1, 2), Pair(2, 3), Pair(1, 9))
listPairs

[(5, 7), (5, 3), (1, 2), (2, 3), (1, 9)]

listPairs.sorted()

error: type parameter bound for T in fun <T : Comparable<T>> Iterable<T>.sorted(): List<T>
 is not satisfied: inferred type Pair<Int, Int> is not a subtype of Comparable<Pair<Int, Int>>
listPairs.sorted()
          ^

sortedBy¶

listPairs.sortedBy{ it.first }

[(1, 2), (1, 9), (2, 3), (5, 7), (5, 3)]

sortedWith¶

listPairs.sortedWith(compareBy({it.first}, {it.second}))

[(1, 2), (1, 9), (2, 3), (5, 3), (5, 7)]

References¶

https://stackoverflow.com/questions/33640864/how-to-sort-based-on-compare-multiple-values-in-kotlin

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

https://www.baeldung.com/kotlin-sort

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.comparisons/natural-order.html