Find maximum-value key in a Kotlin Map

This article explores different ways to find the maximum-value entry in a Kotlin Map.

1. Using `maxBy()` function

The recommended solution is to find the maximum value entry in the map is using the maxWith() function that accepts a Comparator to compare objects based on a field value.

fun main() {

val map: MutableMap<Char, Int> = mutableMapOf(

Pair('A', 1), Pair('B', 2), Pair('C', 3), Pair('D', 4)

)

val maxEntry = map.maxWith(Comparator { x, y -> x.value.compareTo(y.value)})

println(maxEntry)

}

Download Code

Output:

D=4

The above code can be further shortened using the maxBy() function, which returns the first entry yielding the largest value of the provided function or null if there are no entries.

fun main() {

val map: MutableMap<Char, Int> = mutableMapOf(

Pair('A', 1), Pair('B', 2), Pair('C', 3), Pair('D', 4)

)

val maxEntry = map.maxBy { it.value }

println(maxEntry)

}

Download Code

Output:

D=4

2. Using `Collections.max()` function

The Collections.max() function returns the maximum element of the specified collection, according to the order induced by the specified comparator. We can use it with Map.Entry.comparingByValue to find the maximum-value entry in the map, as shown below:

import java.util.Collections

fun main() {

val map: MutableMap<Char, Int> = mutableMapOf(

Pair('A', 1), Pair('B', 2), Pair('C', 3), Pair('D', 4)

)

val maxEntry = Collections.max(map.entries, java.util.Map.Entry.comparingByValue())

println(maxEntry)

}

Download Code

Output:

D=4

3. Using Loop

We can also iterate over the map and keep track of the entry with the maximum value. This can be implemented as follows in Kotlin, using a loop.

fun main() {

val map: MutableMap<Char, Int> = mutableMapOf(

Pair('A', 1), Pair('B', 2), Pair('C', 3), Pair('D', 4)

)

var maxEntry: Map.Entry<Char, Int>? = null

for (entry in map.entries) {

if (maxEntry == null || entry.value > maxEntry.value) {

maxEntry = entry

}

println(maxEntry)

}

Download Code

Output:

D=4

We can also iterate over the Map’s keys to find the key with the maximum value:

fun main() {

val map: MutableMap<Char, Int> = mutableMapOf(

Pair('A', 1), Pair('B', 2), Pair('C', 3), Pair('D', 4)

)

var maxKey: Char? = null

for (key in map.keys) {

if (maxKey == null || map[key]!! > map[maxKey]!!) {

maxKey = key

}

println(maxKey)

}

Download Code

Output:

D

If multiple keys have the maximum value, the above code returns the first key with the maximum value. To get all keys having the maximum value, we can do something like:

fun main() {

val map: MutableMap<Char, Int> = mutableMapOf(

Pair('A', 1), Pair('B', 2), Pair('C', 3), Pair('D', 4)

)

val maxValue = map.values.max()

val maxValueKeys: MutableList<Char> = mutableListOf()

for ((key, value) in map) {

if (value == maxValue) {

maxValueKeys.add(key)

}

println(maxValueKeys)

}

Download Code

Output:

[B, D]

That’s all about finding the maximum-value entry in a Kotlin Map.

Find maximum-value key in a Kotlin Map

1. Using maxBy() function

2. Using Collections.max() function

3. Using Loop

Share this:

1. Using `maxBy()` function

2. Using `Collections.max()` function