ADDITION :
Swift has no DEFINED ORDER for Set and Dictionary.For that reason you should use sorted() method to prevent from getting unexpected results such as your array can be like ["a","b"] or ["b","a"] and you do not want this.
TO FIX THIS:
FOR SETS
var example:Set = ["a","b","c"]
let makeExampleArray = [example.sorted()]
makeExampleArray
Result: ["a","b","c"]
Without sorted()
It can be:
["a","b","c"] or ["b","c","a",] or ["c","a","b"] or ["a","c","b"] or ["b","a","c"] or ["c","b","a"]
simple math : 3! = 6