List in Kotlin

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

Create an Empty List¶

listOf < Int > ()

[]

List(0, {0})

[]

Create a List with Initial Values¶

val list = listOf(0, 1, 2, 3, 4)
list

[0, 1, 2, 3, 4]

Concatenate List with Other Iterables¶

listOf(0, 1, 2) + listOf(3, 4, 5)

[0, 1, 2, 3, 4, 5]

listOf(0, 1, 2) + mutableListOf(3, 4, 5)

[0, 1, 2, 3, 4, 5]

Sort a List¶

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)]

Methods and Operators¶

joinToString¶

listOf(1, 2, 3).joinToString(", ")

1, 2, 3

subList¶

list.subList(1, 3)

[1, 2]

take¶

list.take(3)

[0, 1, 2]

takeLast¶

list.takeLast(2)

[3, 4]

data class is preferred over Tuple-like data.

ceil(2.3)

3.0

References¶

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-mutable-list.html

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/mutable-list-of.html

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-list/index.html

https://stackoverflow.com/questions/33278869/how-do-i-initialize-kotlins-mutablelist-to-empty-mutablelist

https://stackoverflow.com/questions/43114367/difference-between-arrayliststring-and-mutablelistofstring-in-kotlin

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