如何根據存儲在另一個數組中的索引獲取數組的項

Question

我有兩個 arrays：

let a = ["apple","banana","orange","pomelo","kiwi","melon"]
let b = [1, 2, 4]

a包含所有項目， b包含我感興趣的項目的索引。
所以我想創建一個 function 來提取數組b中指定的索引處的項目。

我可以用 for 循環做 tis：

for i in 0...a.count-1{
    if i == b[i]{
    print(a[i])
  }
}

為了清楚起見，所需的 output 將是：

香蕉橙獼猴桃

問題是如果數字很大，for 循環會太慢。
我想知道是否存在復雜性較低的東西。

Answer 1

您可以簡單地 map 索引並返回相關元素：

---

let aa = ["apple","banana","orange","pomelo","kiwi","melon"]
let bb = [1, 2, 4]

let elements = bb.map { aa[$0] }
print(elements)    // ["banana", "orange", "kiwi"]

---

或擴展 RandomAccessCollection 協議：

---

extension RandomAccessCollection {
    func elements(at indices: [Index]) -> [Element] { indices.map { self[$0] } }
}

---

let a = ["apple","banana","orange","pomelo","kiwi","melon"]
let b = [1, 2, 4]

let elements = a.elements(at: b)    // ["banana", "orange", "kiwi"]