How to sort map by value kotlin

KotlinHow-ToBeginner · 3 min read

How to Sort Map by Value in Kotlin: Simple Guide

In Kotlin, you can sort a map by its values using toList() to convert it to a list of pairs, then sortedBy { it.second } to sort by the value. Finally, convert it back to a map with toMap() if needed.

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Syntax

To sort a map by its values in Kotlin, use the following pattern:

map.toList(): Converts the map to a list of key-value pairs.
sortedBy { it.second }: Sorts the list by the value part of each pair.
toMap(): Converts the sorted list back to a map.

kotlin

val sortedMap = map.toList().sortedBy { it.second }.toMap()

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Example

This example shows how to sort a map of names and scores by the scores in ascending order.

kotlin

fun main() {
    val scores = mapOf("Alice" to 50, "Bob" to 75, "Charlie" to 60)
    val sortedScores = scores.toList().sortedBy { it.second }.toMap()
    println(sortedScores)
}

Output

{Alice=50, Charlie=60, Bob=75}

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Common Pitfalls

One common mistake is trying to sort the map directly without converting it to a list first, which is not supported because maps are unordered collections. Another pitfall is expecting the original map to be changed; sorting creates a new map or list.

kotlin

fun main() {
    val map = mapOf("a" to 3, "b" to 1, "c" to 2)
    // Wrong: map.sortedBy { it.value } // This returns a list, not a map

    // Right way:
    val sortedMap = map.toList().sortedBy { it.second }.toMap()
    println(sortedMap)
}

Output

{b=1, c=2, a=3}

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Quick Reference

Remember these key functions for sorting maps by value in Kotlin:

Function	Purpose
`toList()`	Convert map to list of pairs
`sortedBy { it.second }`	Sort list by value
`toMap()`	Convert sorted list back to map

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Key Takeaways

Convert the map to a list before sorting by values using toList().

Use sortedBy { it.second } to sort by the map's values.

Convert the sorted list back to a map with toMap() if you need a map result.

Sorting creates a new collection; the original map stays unchanged.

Maps are unordered, so sorting returns a LinkedHashMap preserving order.