How do I sort an array in Scala?

Question

I can see there\'s a sorting object, Sorting, with a quicksort method, quickSort, on it.

What would be a code example of using it, sorting

Answer 1

val array = Array((for(i <- 0 to 10) yield scala.util.Random.nextInt): _*)
scala.util.Sorting.quickSort(array)

Scala's "default" array is a mutable data structure, very close to Java's Array. Generally speaking, that means an "array" is not very Scala-ish, even as mutable data structures go. It serves a purpose, though. If array is the right data type for your need, then that is how you sort it. There are other sorting methods on object Sorting, by the way.

I think I just realized what your question is... you don't need to pass any implicit parameter (it's implicit, after all). That parameter exists to say that there must be some way to convert the type K into an Ordered[K]. These definitions already exist for Scala's classes, so you don't need them.

For an arbitrary class you can define it this way:

scala> case class Person(name: String)
defined class Person

scala> val array = Array(Person("John"), Person("Mike"), Person("Abe"))
array: Array[Person] = Array(Person(John), Person(Mike), Person(Abe))

scala> scala.util.Sorting.quickSort(array)
:11: error: no implicit argument matching parameter type (Person) => Ordered[Person] was found.
       scala.util.Sorting.quickSort(array)
                                   ^
scala> class OrderedPerson(val person: Person) extends Ordered[Person] {
     | def compare(that: Person) = person.name.compare(that.name)
     | }
defined class OrderedPerson

scala> implicit def personToOrdered(p: Person) = new OrderedPerson(p)
personToOrdered: (p: Person)OrderedPerson

scala> scala.util.Sorting.quickSort(array)

scala> array
res8: Array[Person] = Array(Person(Abe), Person(John), Person(Mike))

Now, if Person was Ordered to begin with, this wouldn't be a problem:

scala> case class Person(name: String) extends Ordered[Person] {
     | def compare(that: Person) = name.compare(that.name)
     | }
defined class Person

scala> val array = Array(Person("John"), Person("Mike"), Person("Abe"))
array: Array[Person] = Array(Person(John), Person(Mike), Person(Abe))

scala>  scala.util.Sorting.quickSort(array)

scala> array
res10: Array[Person] = Array(Person(Abe), Person(John), Person(Mike))