Swift - Collection Types - Array

数组 — Array

通过一个默认值重复创建数组

var threeDoubles = Array(repeating: 0.0, count: 3)
var anotherThreeDoubles = Array(repeating: 0.1, count: 3)

通过两个数组创建一个新的数组

var sixDoubles = threeDoubles + anotherThreeDoubles

通过字面量创建

var shoppingList: [String] = ["Eggs", "Milk"]

由于 Swift 的数据推断，初始化的时候可以不加数据类型

var shoppingListNew = ["Eggs", "Milk"]

访问和修改数组

shoppingList.count
shoppingList.isEmpty
shoppingList.append("Flour")
shoppingList += ["Baking Powder"]
shoppingList += ["Chocolate Spread", "Cheese", "Butter"]
var firstItem = shoppingList[0]
shoppingList[0] = "Six eggs"
shoppingList[4...6] = ["Bananas", "Apples"] // 4.5.6 -> 4.5
shoppingList.insert("Maple Syrup", at: 0)
var returnRemoveString = shoppingList.remove(at: 0)
var returnRemoveLast = shoppingList.removeLast()

遍历

for item in shoppingList {
    print(item)
}

同时获取 index 和 item

for (index, item) in shoppingList.enumerated() {
    print("Item \(index + 1): \(item)")
}

集合 — Set

存储不同值并且相同类型、不排序

Hash Values for Set Types

• 类型必须是以 Hashable 以存储在集合中，Int 类型
• if a == b，a.hashable == b.hashable
• 使用自定义类型作为集合值类型或者字典key类型，遵循 Hashable
• 遵循 Hashable 协议必须提供 get Int hashValue，该值不需要在相同程序或者不同程序的不同执行中相同
• Hashable 遵循 Equatable，所以还必须提供一个 == 操作符的实现
• == 必须满足三个条件：
  （1）a == a 自反性
  （2）a == b 等效于 b == a
  （3）a == b && b == c 等效于 a == c

创建和实例化空集合

var letters = Set<Character>()
letters.insert("a")
letters = []
var favoriteGenres: Set<String> = ["Rock", "Classical", "Hip hop"]
// 不能从一个数组字面量被推断为 Set 数据类型，必须显示声明
// but 不需要写 set 中  的类型
let favoriteGenresNew: Set = ["Rock", "Classical", "Hip hop"]

访问和修改集合

favoriteGenres.count
favoriteGenres.isEmpty
favoriteGenres.insert("Jazz")
if let removedGenre = favoriteGenres.remove("Rock") {
    print("\(removedGenre)? I'm over it")
}else {
    print("I never much cared for that")
}
if favoriteGenres.contains("Funk") {
    print("I get up on the good foot.")
}else {
    print("It's too funky in here")
}

遍历集合

for genre in favoriteGenres {
    print("\(genre)")
}

for genre in favoriteGenres.sorted() { // < 排序
    print("\(genre)")
}

集合操作

var a: Set = Set<String>()
var b: Set = Set<String>()
a.intersection(b) // 交集，共有部分
a.symmetricDifference(b) // 非共有部分总和
a.union(b) // 并集，a + b
a.subtracting(b) // a - a.intersection(b)(交集)
a == b // a 和 b 有所有相同值
a.isSubset(of: b) // a 是不是 b 的子集
a.isSuperset(of: b) // a 是不是 b 的父集
a.isStrictSubset(of: b) // a 是不是 b 的子集，但是不等于 b
a.isStrictSuperset(of: b) // a 是不是 b 的父集，但是不等于 b
a.isDisjoint(with: b) // a 和 b 没有公共部分

字典 — Dictionary

var namesOfIntegers = [Int: String]() // 空数组
namesOfIntegers = [:] // 空数组
var airports: [String: String] = ["YYZ": "Toronto Person", "DUB": "Dublin"] // key: value

访问和修改字典

airports.count
if airports.isEmpty {
    print("The airports dictionary is empty")
} else {
    print("The airports dictionary is not empty")
}

airports["LHR"]  = "London"// 添加一个新值 或 修改值
var returnOldValue = airports.updateValue("London", forKey: "LHR") // 添加一个新值 或 修改值
if let oldValue = airports.updateValue("Dublin Airport", forKey: "DUB") {
    print("The old value for DUB was \(oldValue).")
}

if let airportName = airports["DUB"] {
    print("The name of the airport is \(airportName)")
} else {
    print("The airport is not in the airports dictionary")
}

移除

airports["APL"] = nil
if let removedValue = airports.removeValue(forKey: "DUB") {
    print("The removed airport's name is \(removedValue)")
} else {
    print("The airport dictionary does not contain a value for DUB")
}

遍历

for (airportCode, airportName) in airports {
    print("\(airportCode) : \(airportName)")
}
// 取出 keys, values
for airportCode in airports.keys.sorted() {
    print("Airport code: \(airportCode)")
}

for airportName in airports.values.sorted() {
    print("Airport code: \(airportName)")
}

keys，values 初始化数组

let airportName = [String](airports.values)
let airportCode = [String](airports.keys)