Scala - Sort by Optional fields, with None value last

Question

I have the following class :

final case class PowerDetails (
  [...],
  label: String,
  title: String,
  category: String,
  idCategory: Option[String],
  numCategory: Option[Int]
)

I need to sort a list of PowerDetails like this :

Elements having a value for idCategory and numCategory should be before the None , and ordered by idCategory and then numCategory. As for the None values, they need to be ordered by the fields category , title , label.

If possible, I would like to avoid extending Ordered

final case class PowerDetails (

   ...

) extends Ordered[PowerDetails] {

    override def compare(that: PowerDetails): Int = {
       // Define here the comparison
    }

}

I tried creating an Ordering as below and then use the sorted function, but I'm getting a NullPointerException

  implicit val orderingPowers = optionOrdering.thenComparing(ordering)

  val ordering: Ordering[PowerDetails] = Ordering[(String, String, String)]
    .on[PowerDetails](powerDetail =>
      ( powerDetail.category, powerDetail.title, powerDetail.label))

  val optionOrdering : Ordering[PowerDetails] = Ordering[(Option[String], Option[Int])]
    .on[PowerDetails](powerDetail =>
      (powerDetail.idCategory, powerDetail.numCategory))

Could you please help me find out how to do it ? Thanks.

Have you tried putting `ordering` ahead of `optionOrdering`? — Levi Ramsey, Jan 29 '20 at 18:21

score 3 · Accepted Answer · answered Jan 29 '20 at 19:33

3

Here's another approach also using Ordering.by along with Option's isEmpty, leveraging false < true for the wanted Some/None ordering:

final case class PowerDetails (
  field1: String,
  field2: Int,
  label: String,
  title: String,
  category: String,
  idCategory: Option[String],
  numCategory: Option[Int]
)

implicit val PDOrderer: Ordering[PowerDetails] = Ordering.by{
  case PowerDetails(_, _, label, title, cat, idCat, numCat) =>
    (idCat.isEmpty, idCat, numCat.isEmpty, numCat, cat, title, label)
}

answered Jan 29 '20 at 19:33

Leo C

22,006
3
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Just tried this one. It works like a charm, thanks !! – sewey Jan 29 '20 at 20:08
What is the order of `Some(2).isEmpty` and `Some(6).isEmpty`? – jwvh Jan 29 '20 at 20:11
`Some(2).isEmpty == Some(6).isEmpty`, but `(Some(2).isEmpty, Some(2)) < (Some(6).isEmpty, Some(6))` with the implicit orderer. – Leo C Jan 29 '20 at 21:06

score 2 · Answer 2 · answered Jan 29 '20 at 18:30

2

Would this work for you?

implicit val PDOrd :Ordering[PowerDetails] = Ordering.by(
  pd => (pd.idCategory.getOrElse("~~~~")
       , pd.numCategory.getOrElse(Int.MaxValue)
       , pd.category
       , pd.title
       , pd.label ))

Admittedly "~~~~" isn't the end of the String universe, but it should work in most cases.

answered Jan 29 '20 at 18:30

jwvh

50,871
7
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thanks, but I'd rather not use `getOrElse`. I'll keep it in mind though, if I can't find anything else – sewey Jan 29 '20 at 20:03

Scala - Sort by Optional fields, with None value last

2 Answers2