计算数组数组中的项目？

如果我有一个声明为的对象

let compoundArray = [Array]

是否有一个属性可以给我在compoundArray中包含的所有数组中的字符串数？

我可以通过在每个数组中添加所有项目来实现:

var totalCount = 0
for array in compoundArray {
   totalCount += array.count }
//totalCount = total items in all arrays within compoundArray

但这似乎很笨拙,看起来swift会有一个Array的属性/方法来做到这一点,不是吗？

谢谢!

你可以使用joined或flatMap为此.

运用 joined

let count = compoundArray.joined().count

运用 flatMap

let count = compoundArray.flatMap({$0}).count

您可以使用添加嵌套数组计数

let count = compoundArray.reduce(0) { $0 + $1.count }

大型阵列的性能比较(在发布配置中在MacBook Pro上编译和运行):

let N = 20_000
let compoundArray = Array(repeating: Array(repeating: "String", count: N), count: N)

do {
    let start = Date()
    let count = compoundArray.joined().count
    let end = Date()
    print(end.timeIntervalSince(start))
    // 0.729196012020111
}

do {
    let start = Date()
    let count = compoundArray.flatMap({$0}).count
    let end = Date()
    print(end.timeIntervalSince(start))
    // 29.841913998127
}

do {
    let start = Date()
    let count = compoundArray.reduce(0) { $0 + $1.count }
    let end = Date()
    print(end.timeIntervalSince(start))
    // 0.000432014465332031
}