Swift 4.2:
String to Array
let list = "Karin, Carrie, David"
let listItems = list.components(separatedBy: ", ")
Output : ["Karin", "Carrie", "David"]
Array to String
let list = ["Karin", "Carrie", "David"]
let listStr = list.joined(separator: ", ")
Output : "Karin, Carrie, David"