如何获取数组中元素的索引在第二位？

Question

我有一个数组[a，b，a，c，d]

我可以通过a

获得第一个array.index(where:{$0 is a})的索引

如何获取第二项a的索引？

Answer 1

以下是一些例子：

let xs = ["a", "b", "a", "c", "d"]
let ys = xs.indices.filter { xs[$0] == "a" }
print(ys) // [0, 2]

// or

let zs = xs.enumerated().flatMap { $0.element == "a" ? $0.offset : nil }
print(zs) // [0, 2]