Kotlin Array count()

Kotlin Array count()

In Kotlin, the count() function is used to determine the number of elements in an array that satisfy a given condition. It returns the count as an integer.

This function is useful when you need to find out how many elements in an array meet a specific criterion.

In this tutorial, we’ll explore the syntax of the count() function and provide examples of its usage in Kotlin arrays.

Syntax

The syntax of the count() function is as follows:

fun <T> Array<out T>.count(): Int
fun <T> Array<out T>.count(predicate: (T) -> Boolean): Int

where

Parameter	Description
predicate	[Optional] A function that defines the condition.

If predicate is not specified as argument, then the count() function returns the number of elements in the array.

Examples for Array count() function

1. Using count() to Count Even Numbers

In this example, we’ll use count() to determine the number of even numbers in an array of integers numbersArray.

Kotlin Program

fun main() {
    val numbersArray = arrayOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
    
    // Using count() to count even numbers
    val countEvenNumbers = numbersArray.count { it % 2 == 0 }
    
    // Printing the original array and the result
    println("Numbers: ${numbersArray.joinToString(", ")}")
    println("Count of Even Numbers: $countEvenNumbers")
}

Output

Numbers: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
Count of Even Numbers: 5

2. Using count() to Count Words Starting with ‘A’

In this example, we’ll use count() to find out how many words in an array start with the letter ‘A’.

Kotlin Program

fun main() {
    val wordsArray = arrayOf("apple", "banana", "orange", "avocado", "kiwi")

    // Using count() to count words starting with 'A'
    val countWordsStartingWithA = wordsArray.count { it.startsWith('a') }

    // Printing the original array and the result
    println("Words: ${wordsArray.joinToString(", ")}")
    println("Count of Words Starting with 'a': $countWordsStartingWithA")
}

Output

Words: apple, banana, orange, avocado, kiwi
Count of Words Starting with 'a': 2

3. Using count() to count number of elements in Array

In this example, we’ll use count() to find the number of elements in an array.

Kotlin Program

fun main() {
    val wordsArray = arrayOf("apple", "banana", "orange", "avocado", "kiwi")

    val arrayLength = wordsArray.count()

    println("Array Length : $arrayLength")
}

Output

Array Length : 5

Summary

In this tutorial, we’ve covered the count() function in Kotlin arrays, its syntax, and how to use it to determine the number of elements that satisfy a given condition.