Use the distinct extension function:
val a = arrayOf("a", "a", "b", "c", "c")
val b = a.distinct() // ["a", "b", "c"]
There’s also distinctBy function that allows one to specify how to distinguish the items:
val a = listOf("a", "b", "ab", "ba", "abc")
val b = a.distinctBy { it.length } // ["a", "ab", "abc"]
As @mfulton26 suggested, you can also use toSet, toMutableSet and, if you don’t need the original ordering to be preserved, toHashSet. These functions produce a Set instead of a List and should be a little bit more efficient than distinct.
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