Swift 数组

一, 基本函数

1,dropFirst dropLast 删除前后面元素

let numbers2 = [10, 22, 333, 3334, 3335]
print(numbers2.dropFirst(2))   // Prints "333, 3334, 3335"
print(numbers2.dropFirst(10)) // Prints "[]"
print(numbers2.dropLast(2))

//TODO:第一个元素匹配值为准,第一个满足删除第一个,返回其他,第一个不满足则返回其他全部, 去其他元素
let arr3 = numbers2.drop { (item) -> Bool in
    return item == 10
}
print(arr3) // [22, 333, 3334, 3335]

2,prefix suffix 获取前后面元素

//TODO:获取前几个
print(numbers.prefix(2))  // Prints "[1, 2]"
print(numbers.prefix(10))  // Prints "[1, 2, 3, 4, 5]"
  
//TODO:返回包含初始元素的子序列，直到谓词返回false并跳过其余元素 ,只取第一个元素
let str1 = ["dwdw", "cwcvwv", "aaaa", "dwedewdwe"]
let temp3 = str1.prefix { (item) -> Bool in
    return item == "dwdw"
 }
print(temp3)//  "dwdw"

//TODO:数组后几个
let numbers = [1, 2, 3, 4, 3, 4, 5, 3]
print(numbers.suffix(2))   // Prints "[4, 5]"
print(numbers.suffix(10))  // Prints "[1, 2, 3, 4, 5]"

3, split 分割元素

//TODO: 分割元素,以2作为分割点,不包括2
let line = "BLANCHE: I don't want realism. I want magic!"
print(line.split(separator: " ")) // ["BLANCHE:", "I", "don\'t", "want", "realism.", "I", "want", "magic!"]

//TODO:切割数组,切割次数,s忽略空数组, 2,从前匹配两个空格,其他是一组
let temp5 = line.split(maxSplits: 2, omittingEmptySubsequences: true) { (item) -> Bool in
            return item == " "
        }
print(temp5) // ["BLANCHE:", "I", "don\'t want realism. I want magic!"]

print( line.split(separator: " ", maxSplits: 2, omittingEmptySubsequences: true)) // ["BLANCHE:", "I", "don\'t want realism. I want magic!"]

4,替换 replaceSubrange

 //TODO:范围替换
var nums = [10, 20, 30, 40, 50]
nums.replaceSubrange(1...3, with: repeatElement(1, count: 5))
print(nums) // [10, 1, 1, 1, 1, 1, 50]
nums.replaceSubrange(5...6, with: [100,200])
print(nums) // [10, 1, 1, 1, 1, 100, 200]
nums.replaceSubrange(2...2, with: repeatElement(1000, count: 1))
print(nums) // [10, 1, 1000, 1, 1, 100, 200]
nums[2] = 2000
print(nums) // [10, 1, 2000, 1, 1, 100, 200]

5,满足者替换

//TODO: 从前往后第一个位置替换
var students = ["Ben", "Ivy", "Jordell", "Maxime"]
if let i = students.firstIndex(of: "Maxime") {
    students[i] = "Max"
}
print(students) // Prints "["Ben", "Ivy", "Jordell", "Max"]"

//TODO: 从后往前最后一个位置替换
var students2 = ["Ben", "Ivy", "Jordell", "Ben", "Maxime"]
if let i = students2.lastIndex(of: "Ben") {
     students2[i] = "Benjamin"
}
print(students2)  // Prints "["Ben", "Ivy", "Jordell", "Benjamin", "Max"]"

6,其他简易函数

 //TODO:数组的不同
print(students.difference(from: students2))
let temp6 = students.difference(from: students2) { (objc, item) -> Bool in
        print(objc + item)
        return objc == item
     }
print(temp6.forEach({ (item) in
     print(item)
}))

//TODO:一个数组是否是另个数组的开始
let arr1 = [1,2,3]
let arr2 = [1,2,3,4,5,6,7]
print(arr2.starts(with: arr1))

//TODO:数组相等
print([1,2,3].elementsEqual([2,3,4]))

//TODO:数组包含
print([1,2,3].contains(1))

//TODO:最小值
print(students2.min()!)
//TODO:最大值
print(students2.max()!)

//TODO:升排序
print([3,2,1,4,5,2].sorted())
//TODO:降序
print([3, 2, 1, 4, 5, 2].sorted(by: { (a, b) -> Bool in
    a > b
}))

二, 高阶函数

1, map 遍历

let possibleNumbers = ["1", "2", "three", "///4///", "5"]
//MARK: map,可以对数组中的每一个元素做一次处理
let arr = ["ddk", "asd", "cmd", "sd", "lp"]
let arr2 = arr.map { (item) -> Bool in
    return item.contains("a")
}
print(arr2)

let numbers = [1, 2, 3, 4]
let mapped = numbers.map {
  Array(repeating: $0, count: $0)
}
print(mapped)// [[1], [2, 2], [3, 3, 3], [4, 4, 4, 4]]

//MARK: 非空判断, map可能存在空值,  flatMap确定类型
let mapped2: [Int?] = possibleNumbers.map {
        str in Int(str)
 } // [1, 2, nil, nil, 5]
print(mapped2)

2, flatMap 遍历 如果是不包含nil元素的一维数组的和map的作用效果是一样的，所以推荐使用flatMap

//MARK: flatMap, 可以对数组中的每一个元素做一次处理,并且不存在空值
let arr3 = arr.flatMap { (item) -> [String] in
      return [item + "_js"]
}
print(arr3)

let flatMapped = numbers.flatMap {
   Array(repeating: $0, count: $0)
}
print(flatMapped) // [1, 2, 2, 3, 3, 3, 4, 4, 4, 4]

let test = [1,2,3,4,5]
let result = test.flatMap({ (value) -> [String] in
    return [String(value), String(value * 5)]
})
print(result)

//MARK: 一维转二维
let test2 = [1,2,3,4,5]
let result2 = test2.flatMap({ (value) -> [[String]] in
    return [[String(value), String(value * 5)]]
})
print(result2)

//MARK: 多维转一维
let array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
print(array.flatMap({ $0 }))

3, compactMap filter 过滤nil

let possibleNumbers = ["1", "2", "three", "///4///", "5"]
let compactMapped: [Int] = possibleNumbers.compactMap {
    str in Int(str)
} // [1, 2, 5]
print(compactMapped)
 
//MARK: 过滤元素
let res2 = possibleNumbers.filter { (objc) -> Bool in
    return Int(objc) != nil
}
print(res2) ["1","2","5"]

4, 叠加

 let res = test2.reduce(1000) { (objc, item) -> Int in
   return objc + item
 }
print(res) // 1015

5, 包含

//MARK: - 包含
let res3 = possibleNumbers.contains { (objc) -> Bool in
   return objc == "5"
}
print(res3) //true