Kotlin List.count() Function
The Kotlin List.count() function finds the number of elements matching the given predicate and returns that value.
Syntax of List.count()
The syntax to call List.count() function is
list.count(predicate)
Parameter | Description |
---|---|
predicate | A function which returns a boolean value for a given element. |
Return Value
Value | Scenario |
---|---|
An integer representing the number of matches for predicate | When there are matches in the list for given predicate |
0 | When there are no matches in the list. |
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Example 1: Count Matches in List
In this example, we will take a list of integers, and count the number of even numbers in this list. The predicate is such that, it returns true if the number is even.
Kotlin Program
fun main(args: Array<String>) { val list1 = listOf(2, 8, 5, 7, 9, 6, 10) val predicate: (Int) -> Boolean = {it % 2 == 0} val result = list1.count(predicate) print("Number of matches in the list: $result") }
Output
Number of matches in the list: 4
Example 2: Count Matches in List of Strings
In this example, we will take list of strings, and a predicate which returns true if the string length is 2. We will use list.count() and predicate, to count the number of elements in the list with length 2.
Kotlin Program
fun main(args: Array<String>) { val list1 = listOf("co", "com", "iso", "dev", "io", "in") val predicate: (String) -> Boolean = {it.length == 2} val result = list1.count(predicate) print("Number of matches in the list: $result") }
Output
Number of matches in the list: 3
Conclusion
In this Kotlin Tutorial, we learned how to count the number of matches for a predicate in the given list, using Kotlin List.count() function.