# 15.Array,Set,Dictionary

## 三种集合类型：

* Array
  * 有序数据集合
* Set
  * 无序无重复数据集合
* Dictionary
  * 无序键值对集合

![Img](/files/-MJ_I95x7MmZJFKBO336)

> Swift 中的数组、集合和字典必须明确其中保存的键和值类型，这样就可以避免插入一个错误数据类型的值。同理，对于获取到的值你也可以放心，其数据类型是确定的。

## Set

> 注意 `Swift` 的 `Set` 类型被桥接到 `Foundation` 中的 `NSSet` 类。

### 集合类型的Hash

一个类型想要存储在`Set`中必须是可`Hash`的。该类型必须提供一个方法来计算它的`Hash`值。(`Hashable`协议)

`Swift` 的所有基本类型（比如 `String`、`Int`、`Double` 和 `Bool`）默认都是可哈希化的，可以作为集合值的类型或者字典键的类型。没有关联值的枚举成员值默认也是可哈希化的。

#### 语法

```swift
// 声明
var favoriteGenres: Set<String> = ["Rock", "Classical", "Hip hop"]

// 推断
var favoriteGenres: Set = ["Rock", "Classical", "Hip hop"]
```

## 集合操作

![Img](/files/-MJ_I960h_aqRNjakqZV)

```swift
let oddDigits: Set = [1, 3, 5, 7, 9]
let evenDigits: Set = [0, 2, 4, 6, 8]
let singleDigitPrimeNumbers: Set = [2, 3, 5, 7]

oddDigits.union(evenDigits).sorted()
// [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
oddDigits.intersection(evenDigits).sorted()
// []
oddDigits.subtracting(singleDigitPrimeNumbers).sorted()
// [1, 9]
oddDigits.symmetricDifference(singleDigitPrimeNumbers).sorted()
// [1, 2, 9]
```

![Img](/files/-MJ_I961rN4GI1lTMl9T)

```swift
let houseAnimals: Set = ["🐶", "🐱"]
let farmAnimals: Set = ["🐮", "🐔", "🐑", "🐶", "🐱"]
let cityAnimals: Set = ["🐦", "🐭"]

houseAnimals.isSubset(of: farmAnimals)
// true
farmAnimals.isSuperset(of: houseAnimals)
// true
farmAnimals.isDisjoint(with: cityAnimals)
// true
```


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