sortedBy and sortedWith

Learn sorting with sortedBy and sortedWith.

sortedBy and sortedWith

sortedBy sorts ascending by a selector field and returns a new list. Example: people.sortedBy { it.age } orders ages from small to large. The original list is unchanged; the result is a separate list.

sortedWith takes a Comparator and enables more complex sorting. With compareBy you can define multiple fields: people.sortedWith(compareBy({ it.name }, { it.age })). For descending order use reverse() or sortedByDescending.

sortedWith and compareBy

Use sortedWith when sorting by multiple fields. The compareBy function evaluates sort keys in order: if the first field ties it looks at the second. Example: people.sortedWith(compareBy({ it.team }, { it.name })) sorts by team then by name.

For descending order use compareByDescending or reverseOrder() which returns a Comparator. Use sortedBy for a single simple field and sortedWith for multiple fields or custom comparison. Sorting is stable: equal elements keep their previous order.

Exercise Apply sortedBy and sortedWith

Define data class Person(val name: String, val age: Int). Create listOf(Person("Alex", 30), Person("Sam", 20), Person("Mara", 25)). Sort by age with sortedBy { it.age } and print each with forEach { println(it) }. Then sort by name with sortedWith(compareBy { it.name }).

Show example solution

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

fun main() {
    val people = listOf(Person("Alex", 30), Person("Sam", 20), Person("Mara", 25))
    val byAge = people.sortedBy { it.age }
    byAge.forEach { println(it) }
    val byName = people.sortedWith(compareBy { it.name })
}

Test yourself

What does sortedBy return?
- Modifies the original
- Does not sort
- A new sorted list
- A reversed list
Show answer

A new sorted list — sortedBy produces a new sorted list.

Complete the sortedBy call

people.____ { it.age }

Show answer

people.sortedBy { it.age }

Match the sorting expressions

sortedBy

Single field
sortedWith

Takes Comparator
compareBy

Field order
descending()

Descending

Next lesson: associate and flatMap

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies