Kotlin Set maxOfWithOrNull()
Syntax & Examples

Set.maxOfWithOrNull() extension function

The maxOfWithOrNull() extension function in Kotlin returns the largest value according to the provided comparator among all values produced by the selector function applied to each element in the collection, or null if there are no elements.

Syntax of Set.maxOfWithOrNull()

The syntax of Set.maxOfWithOrNull() extension function is:

fun <T, R> Set<T>.maxOfWithOrNull(comparator: Comparator<in R>, selector: (T) -> R): R?

This maxOfWithOrNull() extension function of Set returns the largest value according to the provided comparator among all values produced by selector function applied to each element in the collection or null if there are no elements.

Parameters

ParameterOptional/RequiredDescription
comparatorrequiredThe comparator used to compare the values.
selectorrequiredA function that takes an element and returns a value to be compared.

Return Type

Set.maxOfWithOrNull() returns value of type R?.


✐ Examples

1 Finding the maximum value among integers with a custom comparator or null if empty

Using maxOfWithOrNull() to find the maximum value among integers in a set with a custom comparator, or null if the set is empty.

For example,

  1. Create a set of integers.
  2. Use maxOfWithOrNull() with a custom comparator and a selector function that transforms each integer.
  3. Print the resulting maximum value or null.

Kotlin Program

fun main() {
    val numbers = setOf(1, 2, 3, 4, 5)
    val maxValue = numbers.maxOfWithOrNull(compareBy { it }, { it.toDouble() })
    println(maxValue)
}

Output

5.0

2 Finding the maximum length of strings with a custom comparator or null if empty

Using maxOfWithOrNull() to find the maximum length among strings in a set with a custom comparator, or null if the set is empty.

For example,

  1. Create a set of strings.
  2. Use maxOfWithOrNull() with a custom comparator and a selector function that returns the length of each string.
  3. Print the resulting maximum length or null.

Kotlin Program

fun main() {
    val strings = setOf("one", "two", "three")
    val maxLength = strings.maxOfWithOrNull(compareBy { it }, { it.length.toDouble() })
    println(maxLength)
}

Output

5.0

3 Finding the maximum age among custom objects with a custom comparator or null if empty

Using maxOfWithOrNull() to find the maximum age among custom objects in a set with a custom comparator, or null if the set is empty.

For example,

  1. Create a data class.
  2. Create a set of custom objects.
  3. Use maxOfWithOrNull() with a custom comparator and a selector function that returns the age of each object.
  4. Print the resulting maximum age or null.

Kotlin Program

data class Person(val name: String, val age: Int)

fun main() {
    val people = setOf(Person("Alice", 30), Person("Bob", 25), Person("Charlie", 35))
    val maxAge = people.maxOfWithOrNull(compareBy { it }, { it.age.toDouble() })
    println(maxAge)
}

Output

35.0

4 Handling an empty set with a custom comparator

Using maxOfWithOrNull() to handle an empty set and return null with a custom comparator.

For example,

  1. Create an empty set of integers.
  2. Use maxOfWithOrNull() with a custom comparator and a selector function that transforms each integer to double.
  3. Print the resulting maximum value or null.

Kotlin Program

fun main() {
    val emptySet = emptySet<Int>()
    val maxValue = emptySet.maxOfWithOrNull(compareBy { it }, { it.toDouble() })
    println(maxValue)
}

Output

null

Summary

In this Kotlin tutorial, we learned about maxOfWithOrNull() extension function of Set: the syntax and few working examples with output and detailed explanation for each example.