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[Swift]遍历集合类型(数组、集合和字典)

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Swift提供了三种主要的集合类型,称为数组,集合和字典,用于存储值集合。

数组是有序的值集合。

集是唯一值的无序集合。

字典是键值关联的无序集合。

../_images/CollectionTypes_intro_2x.png

Swift中无法再使用传统形式的for循环。

1 //传统for循环形式不适用于Swift
2 for(单次表达式;条件表达式;末尾循环体){中间循环体;}

遍历数组:可以使用forin循环遍历数组中的值。

 1 let arrayStr:[String] = ["s","t","r","e","n","g","t","h","e","n","!"]
 2 
 3 //方法1:根据元素顺序遍历
 4 for item in arrayStr {
 5     print(item)
 6 }
 7 
 8 //方法2:根据部分元素顺序遍历
 9 for item in arrayStr[1...5] {
10     print(item)
11 }
12 
13 //方法3:根据索引顺序遍历
14 for index in 0...(arrayStr.count - 1) {
15     print(arrayStr[index])
16 }
17 
18 //方法4:初始化数组并顺序遍历
19 for item in Array(1...10) {
20     print(item)
21 }
22 
23 //方法5:stride函数
24 //from,to,by 最后一个值是 >(或<) to的值
25 //from,through,by 最后一个值是 >=(或<=) through的值
26 for index in stride(from: 0, to: arrayStr.count,by: 1 )
27 {
28     print(arrayStr[index])
29 }

如果不需要序列中的每个值,则可以使用下划线(_)代替变量名来忽略这些值。

1 let base = 3
2 let power = 10
3 var answer = 1
4 for _ in 1...power {
5     answer *= base
6 }
7 print("\(base) to the power of \(power) is \(answer)")
8 // Prints "3 to the power of 10 is 59049"

遍历集合可以使用forin循环遍历集合中的值

1  let arrayStr:Set<String> = ["s","t","r","e","n","g"]
2 //输出的顺序是随机的
3 for item in arrayStr {
4     print("\(item)")
5 }

Swift的Set类型没有定义的顺序。要以特定顺序迭代集合的值,请使用该sorted()方法,该方法将集合的元素作为使用<运算符排序的数组返回

1  let arrayStr:Set<String> = ["s","t","r","e","n","g"]
2 //按照字母排序顺序输出
3 for item in arrayStr.sorted() {
4     print("\(item)")
5 }

遍历字典(可单独遍历键、值、或键值)

可以用字典遍历键值对forin环。字典中的每个项都作为元组返回,您可以将元组的成员分解为临时常量或变量,作为迭代的一部分:(key, value),还可以通过访问字典的键keysvalues属性来检索字典的键或值的可迭代集合:

 1 var direc: [Int: String] =  [0:"s",1:"t",2:"r",3:"e",4:"n",5:"g"]
 2 
 3 //按键值对遍历顺序遍历
 4 for (num, char) in direc.sorted(by: <) {
 5     print("\(num): \(char)")
 6 }
 7 
 8 //按键遍历顺序遍历
 9 for num in direc.keys.sorted(by: <) {
10     print("\(num)")
11 }
12 
13 //按值遍历顺序遍历
14 for char in direc.values {
15     print("\(char)")
16 }

如果您需要使用带有Array实例的API的字典键或值,请使用keysvalues属性初始化新数组

1 let nums = [Int](direc.keys)
2 print(nums)
3 //次序随机 [4, 5, 2, 0, 1, 3]
4 
5 let chars = [String](direc.values)
6 print(chars)
7 //次序随机 ["n", "g", "r", "s", "t", "e"]

Swift的Dictionary类型没有定义的顺序。要按特定顺序迭代字典的键或值,请sorted()在其keysvalues属性使用该方法

倒序遍历 :reversed() 或 stride函数

Swift中标准库中方法

1 //可以用来快速的枚举数组中的内容,并用元组(index, value)接收
2 public func enumerated() -> EnumeratedSequence<Array<Element>>
3 
4 //可以倒叙数组内容
5 public func reversed() -> ReversedRandomAccessCollection<Array<Element>>

当两者结合使用用到索引时需要注意

 1 let arrayStr:[String] = ["s","t","r","e","n","g","t","h","e","n","!"]
 2 
 3 //索引元素值绑定一起倒序遍历
 4 for i in arrayStr.enumerated().reversed() {
 5   print("\(i) ", terminator: "")
 6 }
 7 /*
 8 (offset: 10, element: "!") (offset: 9, element: "n") (offset: 8, element: "e") (offset: 7, element: "h") (offset: 6, element: "t") (offset: 5, element: "g") (offset: 4, element: "n") (offset: 3, element: "e") (offset: 2, element: "r") (offset: 1, element: "t") (offset: 0, element: "s") 
 9 */
10 
11 //只元素值倒序遍历,原索引不变
12 for i in arrayStr.reversed().enumerated() {
13   print("\(i) ", terminator: "")
14 }
15 /*
16 (offset: 0, element: "!") (offset: 1, element: "n") (offset: 2, element: "e") (offset: 3, element: "h") (offset: 4, element: "t") (offset: 5, element: "g") (offset: 6, element: "n") (offset: 7, element: "e") (offset: 8, element: "r") (offset: 9, element: "t") (offset: 10, element: "s") 
17 */

倒序遍历数组

 1 let arrayStr:[String] = ["s","t","r","e","n","g","t","h","e","n","!"]
 2 
 3 //方法1:根据元素倒序遍历
 4 for item in arrayStr.reversed() {
 5     print(item)
 6 }
 7 
 8 //方法2:根据部分元素倒序遍历
 9 for item in arrayStr[1...5].reversed() {
10     print(item)
11 }
12 
13 //方法3:根据索引倒序遍历
14 for index in (0...(arrayStr.count - 1)).reversed() {
15     print(arrayStr[index])
16 }
17 
18 //方法4:初始化数组并倒序遍历
19 for item in Array(1...10).reversed() {
20     print(item)
21 }
22 
23 //方法4:初始化数组并倒序遍历
24 for item in Array(1...10).reversed() {
25     print(item)
26 }
27 
28 //方法5:stride函数
29 //from,to,by 最后一个值是 >(或<) to的值
30 //from,through,by 最后一个值是 >=(或<=) through的值
31 for index in stride(from: arrayStr.count - 1, through: 0,by: -1 )
32 {
33      print(arrayStr[index])
34 }

 倒序遍历集合

1 let arrayStr:Set<String> = ["s","t","r","e","n","g"]
2 //按照字母排序倒序输出
3 for item in arrayStr.sorted().reversed() {
4     print("\(item) ", terminator: "")
5 }
6 //Print "t s r n g e" 

倒序遍历字典(可单独遍历键、值、或键值)

1 var direc: [Int: String] =  [0:"s",1:"t",2:"r",3:"e",4:"n",5:"g"]
2 //按键值对倒序遍历
3 for (num, char) in direc.sorted(by: <).reversed() {
4     print("\(num): \(char)")
5 }

 

posted @ 2018-10-16 15:51  为敢技术  阅读(2089)  评论(0编辑  收藏  举报