Kotlin Tutorials

Kotlin Map minByOrNull()
Syntax & Examples

Syntax of Map.minByOrNull()

The syntax of Map.minByOrNull() extension function is:

fun <K, V, R : Comparable<R>> Map<out K, V>.minByOrNull( selector: (Entry<K, V>) -> R ): Entry<K, V>?

This minByOrNull() extension function of Map returns the first entry yielding the smallest value of the given function or null if there are no entries.


✐ Examples

1 Get entry with the smallest value

In this example,

  • We create a map named map1 with key-value pairs {'apple': 3, 'banana': 1, 'cherry': 2}.
  • We then apply the minByOrNull() function on map1, using the selector { it.value } to compare entries based on their values.
  • As a result, the entry with the smallest value ('banana': 1) is returned.
  • We print the result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map1 = mapOf("apple" to 3, "banana" to 1, "cherry" to 2)
    val result = map1.minByOrNull { it.value }
    println(result)
}

Output

banana=1

2 Get entry with the smallest key

In this example,

  • We create a map named map2 with key-value pairs {1: 'apple', 2: 'banana', 3: 'cherry'}.
  • We then apply the minByOrNull() function on map2, using the selector { it.key } to compare entries based on their keys.
  • As a result, the entry with the smallest key (1: 'apple') is returned.
  • We print the result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map2 = mapOf(1 to "apple", 2 to "banana", 3 to "cherry")
    val result = map2.minByOrNull { it.key }
    println(result)
}

Output

1=apple

3 Get entry with the smallest numeric value

In this example,

  • We create a map named map3 with key-value pairs {'apple': 5, 'banana': 7, 'cherry': 3}.
  • We then apply the minByOrNull() function on map3, using the selector { it.value } to compare entries based on their values.
  • As a result, the entry with the smallest numeric value ('cherry': 3) is returned.
  • We print the result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map3 = mapOf("apple" to 5, "banana" to 7, "cherry" to 3)
    val result = map3.minByOrNull { it.value }
    println(result)
}

Output

cherry=3

Summary

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