Find all occurrences of an element in a Kotlin List

This article explores different ways to find all occurrences of an element in a Kotlin List.

1. Using `filter()` function

To find the indices of all occurrences of an element in a list, you can create a range of the valid indices and apply a filter over it to collect all matching elements with the given value.

fun main() {

val values = listOf("A", "B", "C", "B", "D")

val target = "B"

val indices = values.indices

.filter { values[it] == target }

.toList()

println(indices)

}

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Output:

[1, 3]

The above solution iterates over the list’s indices and not the list. If you need an Int array, use toIntArray() function instead:

fun main() {

val values = listOf("A", "B", "C", "B", "D")

val target = "B"

val indices = values.indices

.filter { values[it] == target }

.toIntArray()

println(indices.contentToString())

}

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Output:

[1, 3]

2. Using Loop

Alternatively, you can write our custom routine for this trivial task using a loop:

fun main() {

val values = listOf("A", "B", "C", "B", "D")

val target = "B"

val indices = mutableListOf<Int>()

for (i in values.indices) {

if (values[i] == target) {

indices.add(i)

}

println(indices)

}

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Output:

[1, 3]

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

Find all occurrences of an element in a Kotlin List

1. Using filter() function

2. Using Loop

1. Using `filter()` function