arrays - 计算数组数组中的项目？

Question

如果我有一个声明为

的对象

let compoundArray = [Array<String>]

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

我可以通过将每个数组中的所有项目相加来做到这一点:

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

但这看起来很笨重，而且 swift 似乎有 Array 的属性/方法来执行此操作，不是吗？

谢谢!

Answer 1

您可以添加嵌套数组计数

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

大型 阵列的性能比较(在发布配置的 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
}