CODEWITHSUNDEEP
scalascala-collections
Yeonho
Yeonho

Reputation: 3623

Specify default value for collections

In scala, is there an idiomatic way to specify default value for collections when it's empty?

For Options, you could use .getOrElse. I'm thinking something like below:

Seq().ifEmpty(Seq("aa", "bb")) // Seq("aa", "bb")
Seq("some", "value").ifEmpty(Seq("aa", "bb")) // Seq("some", "value")

Upvotes: 4

Views: 3330

Answers (3)

dk14
dk14

Reputation: 22374

The cleanest way for scala (without scalaz) seems to be:

Option(list).filter(_.nonEmpty).getOrElse(List(1,2,3))

Upvotes: 4

dk14
dk14

Reputation: 22374

You may try scalaz's toNel (to Non-empty list) - it will give you Some(collection) for non-empty collection and None for empty collection, so you can do list.toNel.getOrElse(List(1)) :

scala> import scalaz._; import Scalaz._
import scalaz._
import Scalaz._

scala> List(1, 2, 3).toNel
res8: Option[scalaz.NonEmptyList[Int]] = Some(NonEmptyList(1, 2, 3))

scala> nil[Int].toNel
res9: Option[scalaz.NonEmptyList[Int]] = None

nil[Int] means List[Int]() here.

Src: http://docs.typelevel.org/api/scalaz/stable/6.0/doc.sxr/scalaz/ListW.scala.html

Upvotes: 0

Eastsun
Eastsun

Reputation: 18869

Is this OK?

scala> val seq = "ABCDEFG".toIndexedSeq
seq: scala.collection.immutable.IndexedSeq[Char] = Vector(A, B, C, D, E, F, G)

scala> seq(3)
res0: Char = D

scala> val ept = Seq.empty[Char]
ept: Seq[Char] = List()

scala> ept(3)
java.lang.IndexOutOfBoundsException: 3
  at scala.collection.LinearSeqOptimized$class.apply(LinearSeqOptimized.scala:51)
  at scala.collection.immutable.List.apply(List.scala:83)
  ... 32 elided

scala> ept.orElse(seq)(3)
res3: Char = D

OR

scala> ept.applyOrElse(3, "abcdef")
res4: Char = d

Upvotes: 1

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