more elegant way to write if( list.nonEmpty) Some(list.max) else None?

Question

List.max returns the "largest" element of a list based on some ordering... But if the list is empty you'll get a java.lang.UnsupportedOperationException: empty.max exception. I don't really like littering code with if statements or matches or whatever. I want something like headOption for max, but I'm not seeing such a method. What's the most elegant way to get the equivalent of list.maxOption?

wouldn't that just move that if-clause somewhere else? – Daniel Figueroa Dec 09 '13 at 22:29 — Daniel Figueroa, Dec 09 '13 at 22:29
put the implementation inside a type class? – colinjwebb Dec 10 '13 at 09:43 — colinjwebb, Dec 10 '13 at 09:43

score 15 · Accepted Answer · edited May 23 '17 at 12:17

15

You can convert a Try into an Option:

Try(empty.max).toOption

You can also use reduceOption (as given in scala - Min/max with Option[T] for possibly empty Seq?):

l.reduceOption(_ max _)

edited May 23 '17 at 12:17

Community

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answered Dec 09 '13 at 22:40

Rob Napier

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Although this option is very elegant, in terms of performance, an `if` is vastly cheaper than opening a `try` block and possibly generating an exception with stack trace. If you case about perf, pick one of the other options. – Leif Wickland Dec 10 '13 at 00:23
I like all these answers, but choosing this one for the link to even more ideas. – nairbv Dec 10 '13 at 15:21

dhg · Answer 2 · 2013-12-09T23:50:57.873

13

Or write your own:

implicit class WithMaxOption[T: Ordering](self: Seq[T]) {
  def maxOption() = if(self.isEmpty) None else Some(self.max)
}

List(1,2,3).maxOption  // Some(3)
List[Int]().maxOption  // None

edited Dec 09 '13 at 23:50

answered Dec 09 '13 at 23:45

dhg

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For my own education: Is there a reason to use `Seq[T]` here rather than `Traversable[T]`? – Rob Napier Dec 10 '13 at 00:59
@Rob, No reason. More general is fine. – dhg Dec 10 '13 at 03:19
I think this is the best answer, pre-2.13. – tilde Apr 21 '20 at 17:00

Xavier Guihot · Answer 3 · 2021-02-04T13:35:08.047

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Starting in Scala 2.13, minOption/maxOption are now part of the standard library:

List(34, 11, 98, 56, 43).maxOption // Option[Int] = Some(98)
List[Int]().maxOption              // Option[Int] = None

edited Feb 04 '21 at 13:35

answered Oct 03 '18 at 06:57

Xavier Guihot

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thoredge · Answer 4 · 2013-12-09T23:45:30.273

8

Here is one way to accomplish it:

Some(list).filter(_.nonEmpty).map(_.max)

edited Dec 09 '13 at 23:45

answered Dec 09 '13 at 23:40

thoredge

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score 1 · Answer 5 · answered Nov 21 '17 at 18:24

1

Another formulation would be

list.headOption.map(_ => list.max)

answered Nov 21 '17 at 18:24

Tim

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I tend to agree!The thing to remember is that the function in a map/filter method doesn't have to use the argument that is passed to it – Tim Nov 22 '17 at 07:51

more elegant way to write if( list.nonEmpty) Some(list.max) else None?

5 Answers5