Scala : Nested getOrElse

Question

I would like to create a method that takes as arguments an array of options and a default value and return the first non empty option otherwise the default value :

def customGetOrElse[T](options : Array[Option[T]], defaultValue : T) : T = {
  // Example if options contain 2 elements
  options(0).getOrElse(options(1).getOrElse(defaultValue))
  // If options contain 3 elements
  options(0).getOrElse(options(1).getOrElse(options(2).getOrElse(defaultValue)))
}

But I am struggling to make this method working for any size of the array. Any ideas ?

Thanks!

score 4 · Accepted Answer · answered Jun 06 '18 at 17:52

4

def customGetOrElse[T](options : Array[Option[T]], defaultValue : T) : T = {
  options.find(_.isDefined).flatten.getOrElse(defaultValue)
}

answered Jun 06 '18 at 17:52

Joe K

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Of course ! I was focused on nesting getOrElse I completely forgot about using find. Thanks ! – Zied Koubaa Jun 06 '18 at 18:10

Nagarjuna Pamu · Answer 2 · 2018-06-06T18:14:38.807

4

The one with collectFirst

def customGetOrElse[T](options: Array[Option[T]], defaultValue: T): T =
 options.collectFirst { case Some(value) => value }.getOrElse(defaultValue)

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scala> :paste
// Entering paste mode (ctrl-D to finish)


 def customGetOrElse[T](options: Array[Option[T]], defaultValue: T): T =
  options.collectFirst { case Some(value) => value }.getOrElse(defaultValue)

// Exiting paste mode, now interpreting.

customGetOrElse: [T](options: Array[Option[T]], defaultValue: T)T

scala> customGetOrElse[Int](Array(None, Some(1)), 2)
res0: Int = 1

scala> customGetOrElse[Int](Array(None, None), 2)
res1: Int = 2

edited Jun 06 '18 at 18:14

answered Jun 06 '18 at 18:04

Nagarjuna Pamu

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Why do you want to fold the whole `Array` even after finding `Some[T]` at the begining ? – sarveshseri Jun 06 '18 at 18:09
@SarveshKumarSingh ur right! edited the answer. `collectFirst` is the way to go – Nagarjuna Pamu Jun 06 '18 at 18:19

score 1 · Answer 3 · answered Jun 06 '18 at 18:08

1

Use flatten over the options to reduce options to those that have a value. Then use headOption to return an Option containing the first value present or None. Lastly, get the value T from the Option or return the defaultValue.

def customGetOrElse[T](options : Array[Option[T]], defaultValue : T) : T = {
  options.flatten.headOption.getOrElse(defaultValue)
}

Examples:

scala> customGetOrElse[Int](Array(None, None), 666)
res29: Int = 666

scala> customGetOrElse[Int](Array(None, Some(42)), 666)
res30: Int = 42

answered Jun 06 '18 at 18:08

Brian

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1

Why flatten the whole Array ? The non-empty option might be the first or second one, that flatten operation itself will be O(n). – sarveshseri Jun 06 '18 at 18:11
Good call. Was just thinking about getting the proper shape of things and not performance. – Brian Jun 06 '18 at 18:23

Scala : Nested getOrElse

3 Answers3

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