我如何获取没有循环的过滤数组中元素的位置

Question

我需要执行以下操作

let array = [1, 2, nil, 3, nil, 4, 5]
var positions: [Int] = []
for (index, val) in array.enumerated() where val == nil {
    positions.append(index)
}
print(positions) //gives [2, 4]

，而不必执行for循环。有可能吗？

Answer 1

过滤indices

let array = [1, 2, nil, 3, nil, 4, 5]
let positions = array.indices.filter{array[$0] == nil}

Answer 2

您可以compactMap枚举：

let array = [1, 2, nil, 3, nil, 4, 5]
let positions = array.enumerated().compactMap { (offset, value) in
    value == nil ? offset : nil
}
print(positions) // [2, 4]