How in Scala to find unique items in List

Question

How in Scala to find unique items in List?

Answer 1

If you refer to the Rosetta Code: Create a Sequence of unique elements

val list = List(1,2,3,4,2,3,4,99)
val l2 = list.removeDuplicates
// l2: scala.List[scala.Int] = List(1,2,3,4,99)

Since List is immutable, you wont modify the initial List by calling removeDuplicates

Warning: as mentioned by this tweet(!), this does not preserve the order:

scala> val list = List(2,1,2,4,2,9,3)
list: List[Int] = List(2, 1, 2, 4, 2, 9, 3)

scala> val l2 = list.removeDuplicates
l2: List[Int] = List(1, 4, 2, 9, 3)

For a Seq, that method should be available in Scala2.8, according to ticket 929.
In the meantime, you will need to define an ad-hoc static method as the one seen here

Answer 2

In 2.8, it's:

List(1,2,3,2,1).distinct  // => List(1, 2, 3)