Count occurrences of each element in a list in Kotlin

This article explores different ways to count occurrences of each element in a list in Kotlin.

1. Using `Collections.frequency()` function

The idea is to call the Collections.frequency() function for each distinct element of the list. It returns the total number of occurrences of the specified element in the list.

import java.util.Collections

fun main() {

val list: List<String?> = listOf("B", "A", "A", "C", "B", "A")

for (item in list.distinct()) {

println(item + ": " + Collections.frequency(list, item))

}

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Output:

B: 2
A: 3
C: 1

2. Using `MutableMap`

Instead of calling the frequency() function for each distinct element, you can construct a MutableMap to store the frequencies of the elements present in a list. This is shown below:

fun main() {

val list = listOf("B", "A", "A", "C", "B", "A")

val frequencyMap: MutableMap<String, Int> = HashMap()

for (s in list)

{

var count = frequencyMap[s]

if (count == null) count = 0

frequencyMap[s] = count + 1

}

println(frequencyMap)

}

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Output:

{A=3, B=2, C=1}

That’s all about counting occurrences of each element in a list in Kotlin.

Count occurrences of each element in a list in Kotlin

1. Using Collections.frequency() function

2. Using MutableMap

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1. Using `Collections.frequency()` function

2. Using `MutableMap`