1.补集(subtracting)

let employees: Set = ["Alicia", "Bethany", "Chris", "Diana", "Eric"]
let neighbors: Set = ["Bethany", "Eric", "Forlani", "Greta"]
let nonNeighbors = employees.subtracting(neighbors)
nonNeighbors 的结果为：”neighbors集合“针对于 ”employees集合“缺少的值，也可以理解结果为”neighbors集合的补集“。
  print("nonNeighbors==>\(nonNeighbors)")
  print("===========")
let nonEmployees = neighbors.subtracting(employees)//与上边相反。
print("nonEmployees==>\(nonEmployees)")

2.交集(intersection)

let iPods: Set = ["iPod touch", "iPod nano", "iPod mini",
"iPod shuffle", "iPod Classic"]
let touchscreen: Set = ["iPhone", "iPad", "iPod touch", "iPod nano"]
let iPodsWithTouch = iPods.intersection(touchscreen)
print("iPodsWithTouch==>\(iPodsWithTouch)")

得到的结果为两个集合共同拥有的部分。

3.并集(formUnion)

let discontinuedIPods: Set = ["iPod mini", "iPod Classic",
"iPod nano", "1"]
var discontinued:Set = ["iBook","Powerbook","Power Mac","1"]
discontinued.formUnion(discontinuedIPods)
//SetAlgebra 协议。
print("discontinued==>\(discontinued)")