Kotlin How to Convert Map to List with Examples

In Kotlin, you can convert a map to a list by using map.toList() which returns a list of pairs, or use map.keys.toList() or map.values.toList() to get lists of keys or values respectively.

Examples

Input{1=10, 2=20}

Output[(1, 10), (2, 20)]

Input{"a"=100, "b"=200}

Output[("a", 100), ("b", 200)]

Input{}

Output[]

How to Think About It

To convert a map to a list in Kotlin, think about what you want: a list of key-value pairs, just keys, or just values. The map itself can be turned into a list of pairs using toList(). If you want only keys or values, convert those collections to lists separately.

Algorithm

1

Get the input map.

2

Decide if you want a list of pairs, keys, or values.

3

If pairs, call <code>toList()</code> on the map.

4

If keys, call <code>keys.toList()</code>.

5

If values, call <code>values.toList()</code>.

6

Return the resulting list.

Code

kotlin

fun main() {
    val map = mapOf(1 to 10, 2 to 20)
    val listPairs = map.toList()
    val listKeys = map.keys.toList()
    val listValues = map.values.toList()
    println(listPairs)   // [(1, 10), (2, 20)]
    println(listKeys)    // [1, 2]
    println(listValues)  // [10, 20]
}

Output

[(1, 10), (2, 20)]
[1, 2]
[10, 20]

Dry Run

Let's trace converting map {1=10, 2=20} to a list of pairs.

1

Start with map

map = {1=10, 2=20}

2

Convert map to list of pairs

listPairs = map.toList() -> [(1, 10), (2, 20)]

3

Print the list

Output: [(1, 10), (2, 20)]

Step	Map	List of Pairs
1	{1=10, 2=20}	N/A
2	{1=10, 2=20}	[(1, 10), (2, 20)]

Why This Works

Step 1: Map to List of Pairs

Using toList() on a map converts each key-value pair into a Pair object inside a list.

Step 2: Keys or Values to List

You can separately convert keys or values collections to lists using keys.toList() or values.toList().

Step 3: Resulting List

The result is a standard Kotlin list you can use like any other list.

Alternative Approaches

Using map.entries.map

kotlin

fun main() {
    val map = mapOf(1 to 10, 2 to 20)
    val list = map.entries.map { it.toPair() }
    println(list)  // [(1, 10), (2, 20)]
}

This creates a list by transforming each map entry explicitly; useful if you want to customize the pair.

Using flatMap for custom list

kotlin

fun main() {
    val map = mapOf(1 to 10, 2 to 20)
    val list = map.flatMap { listOf(it.key, it.value) }
    println(list)  // [1, 10, 2, 20]
}

This flattens keys and values into a single list; useful if you want a combined list of all elements.

Complexity: O(n) time, O(n) space

Time Complexity

Converting a map to a list requires visiting each element once, so it takes linear time relative to the map size.

Space Complexity

A new list is created to hold all pairs or keys/values, so space grows linearly with the map size.

Which Approach is Fastest?

Using toList() is the simplest and fastest for direct conversion; alternatives add overhead for transformations.

Approach	Time	Space	Best For
map.toList()	O(n)	O(n)	Simple direct conversion to list of pairs
map.entries.map { it.toPair() }	O(n)	O(n)	Custom transformation of entries
map.flatMap { listOf(it.key, it.value) }	O(n)	O(n)	Flatten keys and values into one list