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.

Is there a difference between a scala collection and a java one? — Robert Moskal, Jun 17 '16 at 19:00
@RobertMoskal Yes - and in fact scala has two completely separate collections hierarchies: immutable and mutable. — WestCoastProjects, Jun 17 '16 at 19:31

score 28 · Accepted Answer · edited Jun 28 '18 at 07:00

28

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

edited Jun 28 '18 at 07:00

conny

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answered Jun 17 '16 at 19:06

Peter Neyens

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That makes sense... but I'd argue it doesn't make for much readability – conny Jun 28 '18 at 06:53

WestCoastProjects · Answer 2 · 2017-06-02T14:16:23.353

22

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

edited Jun 02 '17 at 14:16

answered Jun 17 '16 at 19:05

WestCoastProjects

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Not sure why it got a downvote. It's the obvious answer – The Archetypal Paul Jun 17 '16 at 19:16
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It could look cleaner as `a.intersect(b).nonEmpty`. – Łukasz Jun 17 '16 at 20:37
The obvious answer is the other one, @TheArchetypalPaul. Anyways, I didn't downvote, just didn't vote. – pedrofurla Jun 17 '16 at 20:47
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 – The Archetypal Paul Jun 17 '16 at 21:11
@Łukasz Thx for the nonEmpty (vs !isEmpty) – WestCoastProjects Jun 17 '16 at 21:59
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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. – conny Jun 28 '18 at 07:01

AJNeufeld · Answer 3 · 2019-08-20T22:40:44.227

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.

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

3 Answers3