Kotlin Tutorials

Kotlin Set maxByOrNull()
Syntax & Examples

Set.maxByOrNull() extension function

The maxByOrNull() extension function in Kotlin returns the first element yielding the largest value of the given function, or null if there are no elements.

Syntax of Set.maxByOrNull()

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

fun <T, R : Comparable<R>> Set<T>.maxByOrNull(selector: (T) -> R): T?

This maxByOrNull() extension function of Set returns the first element yielding the largest value of the given function or null if there are no elements.

Parameters

ParameterOptional/RequiredDescription
selectorrequiredA function that takes an element and returns the value to be compared.

Return Type

Set.maxByOrNull() returns value of type T?.


✐ Examples

1 Finding the maximum element by a property in a set of integers

Using maxByOrNull() to find the maximum element in a set of integers.

For example,

  1. Create a set of integers.
  2. Use maxByOrNull() with a selector function that returns the element itself.
  3. Print the resulting element.

Kotlin Program

fun main() {
    val numbers = setOf(1, 2, 3, 4, 5)
    val maxNumber = numbers.maxByOrNull { it }
    println(maxNumber)
}

Output

5

2 Finding the string with the maximum length in a set

Using maxByOrNull() to find the string with the maximum length in a set.

For example,

  1. Create a set of strings.
  2. Use maxByOrNull() with a selector function that returns the length of each string.
  3. Print the resulting string.

Kotlin Program

fun main() {
    val strings = setOf("one", "two", "three")
    val longestString = strings.maxByOrNull { it.length }
    println(longestString)
}

Output

three

3 Finding the custom object with the maximum age in a set

Using maxByOrNull() to find the custom object with the maximum age in a set.

For example,

  1. Create a data class.
  2. Create a set of custom objects.
  3. Use maxByOrNull() with a selector function that returns the age of each object.
  4. Print the resulting object.

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 oldestPerson = people.maxByOrNull { it.age }
    println(oldestPerson)
}

Output

Person(name=Charlie, age=35)

Summary

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