How to Sort a Map by Keys in Kotlin

How to Sort a Map by Keys in Kotlin ?

Answer

To sort a map by keys in Kotlin, you can use the `toSortedMap` method, which returns a new map with the keys sorted. This method provides a straightforward way to ensure the map is sorted by keys.

✐ Examples

1 Sorting a Map by Keys Using toSortedMap

We can sort a map by keys in Kotlin by using the `toSortedMap` method, which returns a new map with the keys sorted.

For example,

We start by declaring and initializing a map named unsortedMap with some key-value pairs. In this example, the map has integer keys and string values.
We use the toSortedMap method to create a new map named sortedMap that contains the same key-value pairs but with sorted keys.
We print the sorted map to the console using the println function to verify the sorting.

Kotlin Program

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

    // Sort the map by keys
    val sortedMap = unsortedMap.toSortedMap()

    // Print the sorted map
    println("Sorted Map by Keys: $sortedMap")
}

Output

Sorted Map by Keys: {1=one, 2=two, 3=three}

2 Sorting a Map by Keys in Descending Order

We can sort a map by keys in descending order in Kotlin by using the `toSortedMap` method with a custom comparator.

For example,

We start by declaring and initializing a map named unsortedMap with some key-value pairs. In this example, the map has integer keys and string values.
We use the toSortedMap method with a custom comparator to create a new map named sortedMap that contains the same key-value pairs but with keys sorted in descending order.
We print the sorted map to the console using the println function to verify the sorting.

Kotlin Program

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

    // Sort the map by keys in descending order
    val sortedMap = unsortedMap.toSortedMap(compareByDescending { it })

    // Print the sorted map
    println("Sorted Map by Keys (Descending): $sortedMap")
}

Output

Sorted Map by Keys (Descending): {3=three, 2=two, 1=one}

3 Sorting a Map with String Keys

We can sort a map with string keys in Kotlin by using the `toSortedMap` method, which returns a new map with the keys sorted alphabetically.

For example,

We start by declaring and initializing a map named unsortedMap with some key-value pairs. In this example, the map has string keys and integer values.
We use the toSortedMap method to create a new map named sortedMap that contains the same key-value pairs but with keys sorted alphabetically.
We print the sorted map to the console using the println function to verify the sorting.

Kotlin Program

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

    // Sort the map by keys
    val sortedMap = unsortedMap.toSortedMap()

    // Print the sorted map
    println("Sorted Map by Keys: $sortedMap")
}

Output

Sorted Map by Keys: {one=1, three=3, two=2}

Summary

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

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