Finding an item that matches predicate in Scala

Question

I\'m trying to search a scala collection for an item in a list that matches some predicate. I don\'t necessarily need the return value, just testing if the list contains it.

Answer 1

Testing if value matching predicate exists

If you're just interested in testing if a value exists, you can do it with.... exists

scala> val l=(1 to 4) toList
l: List[Int] = List(1, 2, 3, 4)

scala> l exists (_>5)
res1: Boolean = false

scala> l exists (_<2)
res2: Boolean = true

scala> l exists (a => a<2 || a>5)
res3: Boolean = true

Other methods (some based on comments):

Counting matching elements

Count elements that satisfy predicate (and check if count > 0)

scala> (l count (_ < 3)) > 0
res4: Boolean = true

Returning first matching element

Find the first element that satisfies predicate (as suggested by Tomer Gabel and Luigi Plinge this should be more efficient because it returns as soon as it finds one element that satisfies the predicate, rather than traversing the whole List anyway)

scala> l find (_ < 3)
res5: Option[Int] = Some(1) 

// also see if we found some element by
// checking if the returned Option has a value in it
scala> l.find(_ < 3) isDefined
res6: Boolean = true

Testing if exact value exists

For the simple case where we're actually only checking if one specific element is in the list

scala> l contains 2
res7: Boolean = true