Swift学习笔记（04）——Set（集合）

集合的初始化必须显式声明类型，不然会被认为是数组。

//var fruitSet : Set = ["apple", "grape", "banana"]
//var fruitSet = Set(["apple", "grape", "banana"])
//var fruitSet : Set = ["apple", "grape", "banana"]  

空集合

var emptySet : Set = []
var emptySet = Set()

集合的增删改查

获取元素个数

var fruitSet : Set = ["apple", "grape", "banana", "orange", "apple"]
//注：集合中的重复元素是无效的，这点有区别于数组
fruitSet.count  //4 

判空

fruitSet.isEmpty //false
emptySet.isEmpty  //true

包含

fruitSet.contains("grape")  //true
fruitSet.contains("lemon")  //false

遍历

for fruit in fruitSet {
    print(fruit)
}

比较

var fruitSet2 : Set = ["apple", "banana", "grape", "orange"]
fruitSet2 == fruitSet  //true
//集合Set中的元素是无序的，这点也是有区别于数组的

添加元素

fruitSet.insert("mongo")  //["apple", "grape", "banana", "orange", "mongo"]
fruitSet.insert("mongo")  //由于集合中的元素是不会重复的，所以重复添加无效

删除元素

fruitSet.remove("orange")  //["apple", "grape", "banana", "mongo"]
//remove()函数返回值为可选型
if let fruit = fruitSet.remove("orange") {
    print("orange is removed")
}
else {
    print("orange 不存在")  
    //如果删除不存在的元素，remove()函数返回值为nil
}
//清空
//fruitSet.removeAll() 

集合的运算

只有两个集合的元素类型相同时，才能进行下面的各种运算，否则会报错。

并

var set1: Set = ["apple", "milk", "oat"]
var set2: Set = ["apple", "rice", "milk"]
//union()函数并不会改变set1和set2，而是会产生一个新的Set
var set3:Set = set1.union(set2)  //["apple", "milk", "oat", "rice"]

交

var set1: Set = ["apple", "milk", "oat"]
var set2: Set = ["apple", "rice", "milk"]
var set3:Set = set1.intersection(set2)  //["apple", "milk"]

减

var set1: Set = ["apple", "milk", "oat"]
var set2: Set = ["apple", "rice", "milk"]
//suntract()函数没有返回值，直接修改set1
set1.subtract(set2)  //["oat"] 

异或（A异或B，即A并B - A交B）

var set1: Set = ["apple", "milk", "oat"]
var set2: Set = ["apple", "rice", "milk"]
var set3:Set = set1.symmetricDifference(set2)  //["oat", "rice"]

集合之间的关系判断

相离（两个集合是否有交集）

var set1: Set = ["apple", "milk", "oat"]
var set2: Set = ["apple", "rice", "milk"]
var set3:Set = ["cake", "biscuit"]

set1.isDisjoint(with: set2)  //false
set1..isDisjoint(with: set3)  //true

子集与超子集
A是B的子集，即B包含A中的所有元素
A是B的超子集，即B包含A中的所有元素（A是B的子集），且A与B不相等

var set1: Set = ["apple", "milk", "oat"]
var set2: Set = ["apple", "milk"]
var set3: Set = ["apple", "milk", "oat"]
var set4: Set = ["apple", "egg"]

//判断set1是否是set3的子集
set1.isSubset(of: set3)  //true  
set3.isSuperset(of: set1)  //true

//判断set2是否是set1的超子集
set1.isStrictSuperset(of: set2)  //true
set2.isStrictSubset(of: set1)  //true

set1.isSuperset(of: set2)  //true
set2.isSuperset(of: set4)  //false