indexOf in Kotlin Arrays

Question

How do I get the index of a value from a Kotlin array?

My best solution right now is using:

val max = nums.max()
val maxIdx = nums.indices.find({ (i) -> nums[i] == max }) ?: -1

is there a better way?

Answer 1

If you want to get the index of the maximum element you can use 'maxBy' function:

val maxIdx = nums.indices.maxBy { nums[it] } ?: -1

It is more efficient since it will traverse the array only once.

Answer 2

With current Kotlin (1.0) you can use indexOf() extension function on arrays:

val x = arrayOf("happy","dancer","jumper").indexOf("dancer")

All extension functions for arrays are found in the api reference.

In your example:

val maxIdx = nums.indexOf(nums.max())

Answer 3

If you want to find the item based on some predicate, then you can use indexOfFirst and indexOfLast extension functions.

val strings = arrayOf("hello","world","hello")
val firstHelloIndex = strings.indexOfFirst { it == "hello" }
val lastHelloIndex  = strings.indexOfLast  { it == "hello" }