Finding an item that matches predicate in Scala - 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.
In Java, I might do something like:
for ( Object item : collection ) {
if ( condition1(item) && condition2(item) ) {
return true;
}
}
return false;
In Groovy, I can do something like:
return collection.find { condition1(it) && condition2(it) } != null
What's the idiomatic way to do this in Scala? I could of course convert the Java loop style to Scala, but I feel like there's a more functional way to do this.

Answer 1

Use filter:
scala> val collection = List(1,2,3,4,5)
collection: List[Int] = List(1, 2, 3, 4, 5)
// take only that values that both are even and greater than 3
scala> collection.filter(x => (x % 2 == 0) && (x > 3))
res1: List[Int] = List(4)
// you can return this in order to check that there such values
scala> res1.isEmpty
res2: Boolean = false
// now query for elements that definitely not in collection
scala> collection.filter(x => (x % 2 == 0) && (x > 5))
res3: List[Int] = List()
scala> res3.isEmpty
res4: Boolean = true
But if all you need is to check use exists:
scala> collection.exists( x => x % 2 == 0 )
res6: Boolean = true

Answer 2

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

Answer 3

The scala way would be to use exists:
collection.exists(item => condition1(item) && condition2(item))
And since java 8 you can use anyMatch:
collection.stream().anyMatch(item -> condition1(item) && condition2(item));
which is much better than a plain for or foreach.

Answer 4

Filter and exists keywords to get the matching values from Lists
val values = List(1,2,3,4,5,6,7,8,9,10,....,1000) //List -1
val factors= List(5,7) // List -2
//To get the factors of List-2 from List-1
values .filter(a => factors.exists(b => a%b == 0)) //Apply different logic for our convenience
Given code helps to get the matching values from 2 different lists