let array1 = ["a","b","c"]
let array2 = ["a","d"]

let set1:Set<String> = Set(array1)
let set2:Set<String> = Set(array2)

Swift 3.0可以对集合执行以下操作：

firstSet.union(secondSet)// Union of two sets
firstSet.intersection(secondSet)// Intersection of two sets
firstSet.symmetricDifference(secondSet)// exclusiveOr

Swift 2.0可以计算数组参数：

set1.union(array2)       // {"a","c","d"} 
set1.intersect(array2)   // {"a","b"}
set1.subtract(array2)    // {"c"}
set1.exclusiveOr(array2) // {"c","d"}

Swift 1.2可以计算：

set1.union(set2)        // {"a","d"}
set1.intersect(set2)    // {"a","b"}
set1.subtract(set2)     // {"c"}
set1.exclusiveOr(set2)  // {"c","d"}

您可以在文档部分找到更多示例。

感谢Michael Stern在Swift 2.0更新的评论中。