Compare each element of Scala list against rest of elements in the list

Question

I have a list of Custom objects which will be compared against rest of the objects in the same list.

My current approach: Currently i take one element from a the list using foreach loop,run another foreach loop to look through the list for elements that are similar to the taken object.

case class TestOb(name:String,pos:Vector[Int])

val lis:List[TestOb] = null

lis.foreach{i=>
    val ref = i._2
    lis.foreach{j=>
        val current = j._2
        //compare ref and current.
    }
}

Is there any other efficient way to do this iteration in Scala within same list without having two foreach loops?

Answer 1

Have you tried using the for -loop?

for( a <- lis; b <- lis) {
  // do stuff with a and b
}

For further convinience here an easy example to get an idea of the iteration going on behind the scenes:

scala> val list = 1 to 3
list: scala.collection.immutable.Range.Inclusive = Range(1, 2, 3)
scala> for(a <- list; b <- list) println(a+" - "+b)
1 - 1
1 - 2
1 - 3
2 - 1
2 - 2
2 - 3
3 - 1
3 - 2
3 - 3

For what its worth, enzymes solution would be more in line with the functional style scala embraces.

Answer 2

An approach to compare each element in a collection against the rest and to collect those that are similar (here identical by using == in collect ). In order to illustrate the case consider

case class C(i:Int)

and a collection where C(1) has a similar item (equality here),

val xs = Array( C(1),C(2),C(3),C(1),C(4) )

Hence we combine each two items, compare them and collect those similar,

xs.combinations(2).collect { case Array(a,b) if a == b => a }.toArray
Array(C(1))

Note combinations delivers an iterator which is consumed (iterated over) by collect . Also, replace == in collect with a dissimilarity function for comparing items to decide which are similar enough.