根据另一个数组的顺序对数组进行有效排序 [英] efficient sorting of an array based on another array's order

问题描述

假设我有这个:

struct Pet {
    let name: String
}

let pets = [Pet(name: "Z"), Pet(name: "F"), Pet(name: "A"), Pet(name: "E")]
let petNames = ["E", "F", "Z", "A"]

我的预期输出是:

[Pet(name: "E"), Pet(name: "F"), Pet(name: "Z"), Pet(name: "A")]

如何按照petNames'的顺序有效地对pets进行排序?

How do I sort pets efficiently by following petNames' order?

我当前的方法似乎效率很低:

My current method appears to be horribly inefficient:

var sortedPets = [Pet]()
for n in petNames {
    sortedPets.append(pets.first(where: { return $0.name == n })!)
}

我可以使用任何功能方法吗?

Any functional approach that I could use?

推荐答案

效率不高，但可以从功能上解决问题:

Not efficient, but it solves the problem functionally:

let pets2 = pets.sorted{petNames.index(of:$0.name)! < petNames.index(of:$1.name)!}

现在我们知道要执行的操作了，因为字典查找速度很快，所以操作更加精细，但效率更高:

Now that we know what we're after, this is more elaborate but much more efficient, because dictionary lookup is fast:

var d = [String:Int]()
zip(petNames, 0..<petNames.count).forEach { d[$0.0] = $0.1 }
let pets2 = pets.sorted{d[$0.name]! < d[$1.name]!}

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