toSortedMap

Converts this Map to a SortedMap. The resulting SortedMap determines the equality and order of keys according to their natural sorting order.

fun <K : Comparable<K>, V> Map<out K, V>.toSortedMap(): SortedMap<K, V>(source)

fun main() {
    val unsorted = mapOf(5 to "five", 3 to "three", 8 to "eight")
    val sorted: SortedMap<Int, String> = unsorted.toSortedMap()
    println(sorted)  // Output: {3=three, 5=five, 8=eight}
}

Source