Scala Ordered by multiple fields
Option 1: sortBy
Using the sortBy
method, this can be pretty simple:
case class Person(first: String, middle: String, last: String)
val personList = List(Person("john", "a", "smith"), Person("steve", "x", "scott"), Person("bill", "w", "smith"))
personList.sortBy{ case Person(f,m,l) => (l,f,m) }
Option 2: Extend Ordered[Person]
By extending Ordered[Person]
, the class will know how to sort itself, so we get things like sorted
, min
, and max
for free:
case class Person(first: String, middle: String, last: String) extends Ordered[Person] {
def compare(that: Person): Int =
(last compare that.last) match {
case 0 =>
(first compare that.first) match {
case 0 => middle compare that.middle
case c => c
}
case c => c
}
}
val personList = List(Person("john", "a", "smith"), Person("steve", "x", "scott"), Person("bill", "w", "smith"))
personList.sorted
personList.min
personList.max
Option 3: Implicit Ordering
If you use an implicit Ordering
, then you get sorted
, min
, etc without having that particular ordering tied to your original class. This decoupling might be convenient, or it might by annoying, depending on your specific case.
case class Person(first: String, middle: String, last: String)
implicit val ord = new Ordering[Person] {
def compare(self: Person, that: Person): Int =
(self.last compare that.last) match {
case 0 =>
(self.first compare that.first) match {
case 0 => self.middle compare that.middle
case c => c
}
case c => c
}
}
val personList = List(Person("john", "a", "smith"), Person("steve", "x", "scott"), Person("bill", "w", "smith"))
personList.sorted
personList.min
personList.max
If you are using scala 2.13+ you can use Ordering.by
and orElseBy
. It is quite explicit.
case class Person(first: String, middle: String, last: String)
implicit val ordering: Ordering[Person] = Ordering.by[Person, String](_.first)
.orElseBy(_.middle)
.orElseBy(_.last)
val list = List(Person("john", "a", "smith"), Person("steve", "x", "scott"), Person("bill", "w", "smith"))
list.sorted