Min/max with Option[T] for possibly empty Seq?

Question

I\'m doing a bit of Scala gymnastics where I have Seq[T] in which I try to find the \"smallest\" element. This is what I do right now:

val leastOrNo         


        

Answer 1

Starting Scala 2.13, minByOption/maxByOption is now part of the standard library and returns None if the sequence is empty:

seq.minByOption(_.something)

List((3, 'a'), (1, 'b'), (5, 'c')).minByOption(_._1) // Option[(Int, Char)] = Some((1,b))
List[(Int, Char)]().minByOption(_._1)                // Option[(Int, Char)] = None

Answer 2

Also, it is available to do like that

Some(seq).filter(_.nonEmpty).map(_.minBy(_.something))

Answer 3

How about this?

import util.control.Exception._
allCatch opt seq.minBy(_.something)

Or, more verbose, if you don't want to swallow other exceptions:

catching(classOf[UnsupportedOperationException]) opt seq.minBy(_.something)

Alternatively, you can pimp all collections with something like this:

import collection._

class TraversableOnceExt[CC, A](coll: CC, asTraversable: CC => TraversableOnce[A]) {

  def minOption(implicit cmp: Ordering[A]): Option[A] = {
    val trav = asTraversable(coll)
    if (trav.isEmpty) None
    else Some(trav.min)
  }

  def minOptionBy[B](f: A => B)(implicit cmp: Ordering[B]): Option[A] = {
    val trav = asTraversable(coll)
    if (trav.isEmpty) None
    else Some(trav.minBy(f))
  }
}

implicit def extendTraversable[A, C[A] <: TraversableOnce[A]](coll: C[A]): TraversableOnceExt[C[A], A] =
  new TraversableOnceExt[C[A], A](coll, identity)

implicit def extendStringTraversable(string: String): TraversableOnceExt[String, Char] =
  new TraversableOnceExt[String, Char](string, implicitly)

implicit def extendArrayTraversable[A](array: Array[A]): TraversableOnceExt[Array[A], A] =
  new TraversableOnceExt[Array[A], A](array, implicitly)

And then just write seq.minOptionBy(_.something).

Answer 4

seq.reduceOption(_ min _)

does what you want?

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Edit: Here's an example incorporating your _.something:

case class Foo(a: Int, b: Int)
val seq = Seq(Foo(1,1),Foo(2,0),Foo(0,3))
val ord = Ordering.by((_: Foo).b)
seq.reduceOption(ord.min)  //Option[Foo] = Some(Foo(2,0))

or, as generic method:

def minOptionBy[A, B: Ordering](seq: Seq[A])(f: A => B) = 
  seq reduceOption Ordering.by(f).min

which you could invoke with minOptionBy(seq)(_.something)