(实验)swift数组高级使用案例

Drop的使用

貌似这个不怎么常用,上代码

var list:[Int] = [1,2,3,4,5,6,7,8,10]
let arr = list.drop { (item) -> Bool in
                print("item:\(item)")
                return  item < 5
            }
print(list)
print(arr)

输出

item:1
item:2
item:3
item:4
item:5
[1, 2, 3, 4, 5, 6, 7, 8, 10]
[5, 6, 7, 8, 10]

drop函数是在闭包中去匹配是否符号,只要不符合后面就不执行了,符合的话会一直执行下去,我们把上面的item < 5改成item > 5

var list:[Int] = [1,2,3,4,5,6,7,8,10]
let arr = list.drop { (item) -> Bool in
                print("item:\(item)")
                return  item > 5
            }
print(list)
print(arr)

输出

item:1
[1, 2, 3, 4, 5, 6, 7, 8, 10]
[1, 2, 3, 4, 5, 6, 7, 8, 10]

可见drop的闭包只执行了一次

数组累加

let numbers = [1,2,3,4,5]
let sum = numbers.reduce(0) { total, num in
    return total + num
}
print(sum)

输出

对每个元素操作,返回一个新的数组

var list:[Int] = [1,2,3,4,5,6,7,8,10]
let newArr = list.map {(number: Int) -> Int in
    return number * number
}
print(newArr)

输出

[1, 4, 9, 16, 25, 36, 49, 64, 100]

过滤数组中需要的元素,返回一个新的数组

var list:[Int] = [1,2,3,4,5,6,7,8,10]
let newArr = list.filter { (number:Int) -> Bool in
    return number % 2 == 0
}
print(newArr)

输出

[2, 4, 6, 8, 10]

把二维数组拍扁

let array = [[1,2,3], [4,5,6], [7,8,9]]
let arrayFlatMap = array.flatMap { $0 }
print(arrayFlatMap)

输出

[1, 2, 3, 4, 5, 6, 7, 8, 9]

上面的代码也可以写成这样

let array = [[1,2,3], [4,5,6], [7,8,9]]
let arrayFlatMap = array.flatMap { (item: [Int]) -> [Int] in
    return item
}
print(arrayFlatMap)

用reduce也能实现,不过很少这么用

let array = [[1,2,3], [4,5,6], [7,8,9]]
let arrayFlatMap = array.reduce([]) { (total, num:[Int]) -> [Int] in
    return total + num
}
print(arrayFlatMap)

能拍扁的不一定是二位数组,想把一个对象的内部的一个变量数组全部取出来可以类似这样,这个经常会用到

var list:[(key:String,value:[Int])] = []
list.append((key: "calss1", value: [1,2,3,4,5,6]))
list.append((key: "calss2", value: [7,8,9,10]))
list.append((key: "calss2", value: [11,12,13,14]))
let arrayFlatMap = list.flatMap { (item:(key:String,value:[Int])) -> [Int] in
    return item.value
}
print(arrayFlatMap)

输出

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]