swift Array map/flatmap/compactmap/filter/reduce/chaining用法小结

import UIKit



let arr = [1,2,3]



//MARK:map(映射)：returns an Array containing results of applying a transform to each item.

arr.map { (value) -> Int in

   return value \* 2

}



arr.map { (value) -> Int in

    value \* 2

}



//闭包写在一行时，执行4次，第一次是闭包赋值操作

arr.map { (value) in value \* 2}



let arr1 = arr.map {

    $0 \* 2

}



arr.map {$0 \* 2}



let arr2 = arr.map {"\($0)"}

print(arr2)



let dic = ["point1" : 10, "point2" : 20, "point3" : 30]

dic.map { (name,distance) -> Int in//参数是元组

    distance \* 2

}

dic.map {$0.1 \* 2}



//MARK:filter：returns an Array containing only those items that match an include condition.

let arrF0 = arr.filter { (num) -> Bool in

    num % 2 == 0

}



let arrF1 = arr.filter { $0 % 2 == 0 }

print(arrF1)



//MARK:reduce（归纳）：初始值+闭包("+"操作符本质也是闭包)。returns a single value calculated by calling a combine closure for each item with an initial value.

let sum = arr.reduce(10) {Result,num -> Int in

    Result + num

}

let sum1 = arr.reduce(10,+)



let dicR0 = dic.reduce("res:") { (Result, arg1) -> String in

    let (key, value) = arg1

    return Result + key + "\(value)" + ","

}



let dicR1 = dic.reduce("res:") { (Result, arg1) -> String in

    let (key, value) = arg1

    return key + "\(value)" + "!"

}



let arrStr = ["你", "好", "啊"]

let dicRStr0 = arrStr.reduce("归纳:"){res, str in res + str}

let dicRStr1 = arrStr.reduce("归纳:", +)



//MARK:flatMap（压平）:二维数组降维成一维；可选值转换为可选值

let arrWithArr = [[1, 2], [3, 4, 5], [6, 7]]

let arrFm = arrWithArr.flatMap{$0}

print(arrFm)



let num: Int? = Int(8);

let numFM = num.flatMap{$0 < 5 ? $0 : nil}



//MARK:compactMap（紧凑）:去 nil+变非可选

let arrWithNil: [String?] = ["1", nil, "2", nil]



//'flatMap' is deprecated: Please use compactMap(\_:) for the case where closure returns an optional value

//arrWithNil.flatMap{$0}



let arrCm = arrWithNil.compactMap{$0}

print(arrCm)

 

//MARK:chaining（链式语法）

let resCh = arrWithArr.flatMap{$0}.filter{$0 > 5}.reduce(10, +)

print(resCh)