Sorting Collections by Multiple Fields in Kotlin: A Comprehensive Guide

 To sort a collection by multiple fields in Kotlin, you can use the sortedWith function along with a custom comparator. Here's an example:

data class Person(val name: String, val age: Int)

fun main() {
    val people = listOf(
        Person("John", 25),
        Person("Alice", 30),
        Person("Bob", 20),
        Person("Alice", 25),
        Person("John", 30)
    )

    val sortedPeople = people.sortedWith(compareBy(Person::name, Person::age))

    for (person in sortedPeople) {
        println("${person.name}, ${person.age}")
    }
}

In this example, we have a Person class with two fields: name and age. We create a list of Person objects called people.

To sort the people list by both name and age, we use the sortedWith function and pass it a comparator created using the compareBy function. The compareBy function takes the properties or fields that you want to sort by, in the order of priority. In this case, we sort by name first and then by age.

The resulting sortedPeople list will be sorted based on the defined criteria. We then iterate over the sorted list and print the name and age of each person.

The output of the above code will be:

Alice, 25
Alice, 30
Bob, 20
John, 25
John, 30

As you can see, the list is sorted first by name in ascending order and then by age in ascending order within each name group.