Find index of an element in a Kotlin List

This article explores different ways to find the index of an element in a Kotlin List.

1. Using `indexOf()` function

The recommended solution to get the index of an element in a list is with the indexOf() library function. It returns the index of the first occurrence of the provided element in the list, or -1 if the element is not present.

fun main() {

val values = listOf(4, 7, 2, 5, 1, 9, 5, 3)

val item = 5

val index = values.indexOf(item)

println(index) // 3

}

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2. Using `withIndex()` function

The idea here is to get an iterable containing the index of each element of the list and the element itself using the withIndex() function. Then return the index of the first pair that match the given value. This would translate to the following code:

fun main() {

val values = listOf(4, 7, 2, 5, 1, 9, 5, 3)

val item = 5

val index = values.withIndex()

.first { item == it.value }

.index

println(index) // 3

}

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3. Using `find()` function

Another viable alternative is to filter the indices containing the given element using the find() function, which returns the first element matching the given predicate, or null if no such element exists. This would translate to a simple code below:

fun main() {

val values = listOf(4, 7, 2, 5, 1, 9, 5, 3)

val item = 5

val index = values.indices.find { values[it] == item }

println(index) // 3

}

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4. Using Loop

Following is an equivalent version using the for loop, which returns the index of the first occurrence, or -1 if no matching element is found.

fun findIndex(values: List<Int>, item: Int): Int {

for (i in values.indices) {

if (values[i] == item) {

return i

}

return -1

}

fun main() {

val values = listOf(4, 7, 2, 5, 1, 9, 5, 3)

val item = 5

val index = findIndex(values, item)

println(index) // 3

}

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That’s all about finding the index of an element in a Kotlin List.

Find index of an element in a Kotlin List

1. Using indexOf() function

2. Using withIndex() function

3. Using find() function

4. Using Loop

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1. Using `indexOf()` function

2. Using `withIndex()` function

3. Using `find()` function