In Scala how do I remove duplicates from a list?

Have a look at the ScalaDoc for Seq,

scala> dirty.distinct
res0: List[java.lang.String] = List(a, b, c)

Update. Others have suggested using Set rather than List. That's fine, but be aware that by default, the Set interface doesn't preserve element order. You may want to use a Set implementation that explicitly does preserve order, such as collection.mutable.LinkedHashSet.

Before using Kitpon's solution, think about using a Set rather than a List, it ensures each element is unique.

As most list operations (foreach, map, filter, ...) are the same for sets and lists, changing collection could be very easy in the code.

scala.collection.immutable.List now has a .distinct method.

So calling dirty.distinct is now possible without converting to a Set or Seq.