Scala Language Sort A List


Example

Supposing the following list we can sort a variety of ways.

val names = List("Kathryn", "Allie", "Beth", "Serin", "Alana")

The default behavior of sorted() is to use math.Ordering, which for strings results in a lexographic sort:

names.sorted
// results in: List(Alana, Allie, Beth, Kathryn, Serin)

sortWith allows you to provide your own ordering utilizing a comparison function:

names.sortWith(_.length < _.length)
// results in: List(Beth, Allie, Serin, Alana, Kathryn)

sortBy allows you to provide a transformation function:

//A set of vowels to use
val vowels = Set('a', 'e', 'i', 'o', 'u')

//A function that counts the vowels in a name
def countVowels(name: String) = name.count(l => vowels.contains(l.toLower))

//Sorts by the number of vowels
names.sortBy(countVowels)
//result is: List(Kathryn, Beth, Serin, Allie, Alana)

You can always reverse a list, or a sorted list, using `reverse:

names.sorted.reverse
//results in: List(Serin, Kathryn, Beth, Allie, Alana)

Lists can also be sorted using Java method java.util.Arrays.sort and its Scala wrapper scala.util.Sorting.quickSort

java.util.Arrays.sort(data)
scala.util.Sorting.quickSort(data)

These methods can improve performance when sorting larger collections if the collection conversions and unboxing/boxing can be avoided. For a more detailed discussion on the performance differences, read about Scala Collection sorted, sortWith and sortBy Performance.