How to Iterate Over Keys in a Map in Kotlin - Step by Step Examples

How to Iterate Over Keys in a Map in Kotlin ?

Answer

To iterate over keys in a map in Kotlin, you can use the keys property along with a for loop or the forEach method. This allows you to access each key in the map.

✐ Examples

1 Iterating Over Keys Using for Loop

We can iterate over keys in a map in Kotlin using a for loop with the keys property, which provides a convenient syntax for iterating over all keys in the map.

For example,

We start by declaring and initializing a map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We use the keys property to get a set of the keys in the map.
We iterate over the keys using a for loop, accessing each key directly from the set.
We print each key to the console using the println function to verify that we are iterating over all keys.

Kotlin Program

fun main() {
    // Declare and initialize a map
    val myMap = mapOf(
        "one" to 1,
        "two" to 2,
        "three" to 3
    )

    // Iterate over keys using for loop
    for (key in myMap.keys) {
        println(key)
    }
}

Output

one
two
three

2 Iterating Over Keys Using forEach Method

We can iterate over keys in a map in Kotlin using the forEach method, which provides a flexible way to access each key in the map.

For example,

We start by declaring and initializing a map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We use the forEach method to iterate over the key-value pairs in the map.
In the lambda expression passed to forEach, we access each key.
We print each key to the console using the println function to verify that we are iterating over all keys.

Kotlin Program

fun main() {
    // Declare and initialize a map
    val myMap = mapOf(
        "one" to 1,
        "two" to 2,
        "three" to 3
    )

    // Iterate over keys using forEach method
    myMap.forEach { (key, _) ->
        println(key)
    }
}

Output

one
two
three

3 Storing and Iterating Over Keys Separately

We can store keys in a separate list and then iterate over the list in Kotlin, which provides a way to work with keys independently of their values.

For example,

We start by declaring and initializing a map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We declare a list named keys to store the keys from the map.
We use the keys property to get a set of the keys in the map and convert it to a list using the toList method.
We use a for loop to iterate over the keys list and print each key to the console using the println function to verify that we have stored all keys separately.

Kotlin Program

fun main() {
    // Declare and initialize a map
    val myMap = mapOf(
        "one" to 1,
        "two" to 2,
        "three" to 3
    )

    // Store keys in a separate list
    val keys = myMap.keys.toList()

    // Iterate over the keys list
    for (key in keys) {
        println(key)
    }
}

Output

one
two
three

Summary

In this tutorial, we learned How to Iterate Over Keys in a Map in Kotlin language with well detailed examples.

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