[ACCEPTED]-How to find a matching element in a list and map it in as an Scala API method?-scala-2.8
How about using collect?
// Returns List(66)
List(1, 2, 3) collect { case i if (i * 33 % 2 == 0) => i * 33 }
However that will 9 return all matches and not just the first one.
The 8 better answer would have been, based on 7 Scala 2.9:
// Returns Some(66)
List(1, 2, 3) collectFirst { case i if (i * 33 % 2 == 0) => i * 33 }
The solution suggested in the 6 comments to append a head to get a Scala 2.8 5 version of that is not very efficient, I'm 4 afraid. Perhaps in that case I would stick 3 to your own code. In any case, in order 2 to make sure it returns an option, you should 1 not call head, but headOption.
// Returns Some(66)
List(1, 2, 3) collect { case i if (i * 33 % 2 == 0) => i * 33 } headOption
If you don't want to do your map() operation 4 multiple times (for instance if it's an 3 expensive DB lookup) you can do this:
l.view.map(_ * 33).find(_ % 2 == 0)
The 2 view makes the collection lazy, so the number 1 of map() operations is minimized.
Hey look, it's my little buddy findMap again!
/**
* Finds the first element in the list that satisfies the partial function, then
* maps it through the function.
*/
def findMap[A,B](in: Traversable[A])(f: PartialFunction[A,B]): Option[B] = {
in.find(f.isDefinedAt(_)).map(f(_))
}
Note 4 that, unlike in the accepted answer, but 3 like the collectFirst method mentioned in one of its 2 comments, this guy stops as soon as he finds 1 a matching element.
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