Kotlin List.indexOfLast() Examples

Kotlin List indexOfLast()

The indexOfLast() function in Kotlin is used to find the index of the last element in a list that matches a given predicate.

Syntax

The indexOfLast() function takes a predicate as input and returns the index of the last element in the list that satisfies the predicate. If no element matches the predicate, it returns -1.

fun <T> List<T>.indexOfLast(predicate: (T) -> Boolean): Int

Parameters

Parameter	Description
predicate	A function that takes an element of type T and returns true if the element matches the criteria, false otherwise.

Return Value

The indexOfLast() function returns the index of the last element that matches the predicate. If no element matches, it returns -1.

Example 1: Finding the Index of Last Even Number

This example demonstrates how to use indexOfLast() to find the index of the last even number in a list.

In this example,

1. Create a list of numbers in the variable numbers.
2. Define a predicate function that checks if a number is even.
3. Call indexOfLast() on the list numbers with the predicate function.
4. The indexOfLast() function returns the index of the last even number in the list.

Kotlin Program

fun main() {
    val numbers = listOf(1, 3, 5, 2, 4, 6)
    val index = numbers.indexOfLast { it % 2 == 0 }
    println("Index of last even number: $index")
}

Output

Example 2: Finding Index of Last String Starting with “A”

In this example, we find the index of the last string in a list that starts with the letter “A”.

In this example,

1. Create a list of strings in the variable names.
2. Define a predicate function that checks if a string starts with the letter “A”.
3. Call indexOfLast() on the list names with the predicate function.
4. The indexOfLast() function returns the index of the last string starting with “A” in the list.

Kotlin Program

fun main() {
    val names = listOf("Alice", "Bob", "Anna", "John")
    val index = names.indexOfLast { it.startsWith("A") }
    println("Index of last name starting with 'A': $index")
}

Output

Summary

The indexOfLast() function in Kotlin is useful for finding the index of the last element in a list that matches a given predicate. We have seen examples of using it with different criteria.