How to Iterate Over Map in Kotlin: Simple Examples

To iterate over a Map in Kotlin, use a for loop with destructuring syntax like for ((key, value) in map). You can also iterate over map.keys or map.values separately depending on your needs.

Syntax

Use a for loop with destructuring to get both key and value from the map entries.

• key: the map key
• value: the map value

Alternatively, iterate over map.keys or map.values to get only keys or values.

kotlin

for ((key, value) in map) {
    // use key and value
}

// Or iterate keys only
for (key in map.keys) {
    // use key
}

// Or iterate values only
for (value in map.values) {
    // use value
}

Example

This example shows how to iterate over a map and print each key and value pair.

kotlin

fun main() {
    val map = mapOf("apple" to 3, "banana" to 5, "orange" to 2)

    for ((key, value) in map) {
        println("Key: $key, Value: $value")
    }
}

Output

Key: apple, Value: 3
Key: banana, Value: 5
Key: orange, Value: 2

Common Pitfalls

A common mistake is to iterate over map without destructuring, which gives Map.Entry objects that need explicit access to key and value.

Also, trying to modify a map while iterating over it can cause errors.

kotlin

fun main() {
    val map = mapOf("a" to 1, "b" to 2)

    // Iterating without destructuring and printing using entry.key and entry.value
    for (entry in map) {
        // entry is Map.Entry, so use entry.key and entry.value
        println("Key: ${entry.key}, Value: ${entry.value}")
    }

    // Using destructuring
    for ((key, value) in map) {
        println("Key: $key, Value: $value")
    }
}

Output

Key: a, Value: 1
Key: b, Value: 2
Key: a, Value: 1
Key: b, Value: 2

Quick Reference

Here is a quick summary of ways to iterate over a Kotlin map:

Method	Description	Example
Destructuring in for loop	Get key and value together	for ((k,v) in map) { ... }
Iterate keys	Get only keys	for (k in map.keys) { ... }
Iterate values	Get only values	for (v in map.values) { ... }
Iterate entries	Use Map.Entry objects	for (entry in map) { entry.key, entry.value }

Key Takeaways

Use for ((key, value) in map) to iterate over keys and values together.

You can iterate keys or values separately using map.keys or map.values.

Map entries can be accessed as Map.Entry objects if not destructured.

Avoid modifying a map while iterating over it to prevent errors.

Destructuring makes code cleaner and easier to read when iterating maps.