How to check if collection contains any element from other collection in Scala?

Question

Title says it all, what is the best practice for finding out if collection contains any element of other collection?

In java I would execute it like this

CollectionUtils.containsAny(a, b)

using common apache collection utils, where variables a/b are collections.

How to implement this behavior in scala? Or is there library like CollectionUtils from above?

I dont want to use the common-apache library because i would have to convert scala collection to java collection.

Solution 1

You can use a combination of exists(p: T => Boolean):Boolean and contains(elem: A1):Boolean :

val a = List(1,2,3,4,5,6,7)
val b = List(11,22,33,44,55,6)

a.exists(b.contains) // true

Solution 2

Intersect

val a = Seq(1,2,3) ; val b = Seq(2,4,5)
a.intersect(b)
res0: Seq[Int] = List(2)

// to include the test:
a.intersect(b).nonEmpty  // credit @Lukasz

Solution 3

Using disjoint() from the standard Java Collections utilities can determine if two collections contain any common members. If the collections are not disjoint, then they contain at least one common element.

Internally, Collections.disjoint() checks if either collection is a Set and optimizes accordingly.

import collection.JavaConverters._

val a = List(1,2,3,4,5,6,7)
val b = List(11,22,33,44,55,6)

!java.util.Collections.disjoint(a.asJava, b.asJava)  // true

Although this is still converting the Scala collection to a Java collection. On the plus side, the extra apache commons library isn't needed.

Comments

[Alexander Aleksandrovič Klimov]

Not sure why it got a downvote. It's the obvious answer

[Łukasz]

It could look cleaner as a.intersect(b).nonEmpty.

[pedrofurla]

The obvious answer is the other one, @TheArchetypalPaul. Anyways, I didn't downvote, just didn't vote.

[Alexander Aleksandrovič Klimov]

Since the question is actually "do the two arrays have any elements in common" I still feel intersect of the obvious answer. It certainly didn't need a down vote. Imo obviously

[WestCoastProjects]

@Łukasz Thx for the nonEmpty (vs !isEmpty)

[conny]

That makes sense... but I'd argue it doesn't make for much readability 😳

[conny]

Isn't it wasteful to have to create an intersection just to check whether it is nonEmpty? I think that is why people vote for the other solution.