How to transpose an array more Swiftly?

Question

I asked a similar question a while ago. It was asking how can I turn an array like this:

[[1,2,3],[4,5,6],[7,8,9]]

to this:

Answer 1

Here's an improvement on Shadow Of's answer:

extension Collection where Self.Iterator.Element: RandomAccessCollection {
    // PRECONDITION: `self` must be rectangular, i.e. every row has equal size.
    func transposed() -> [[Self.Iterator.Element.Iterator.Element]] {
        guard let firstRow = self.first else { return [] }
        return firstRow.indices.map { index in
            self.map{ $0[index] }
        }
    }
}

let matrix = [
    [1, 2, 3, 4],
    [5, 6, 7, 8],
    [9, 10, 11, 12],
]
matrix.transposed().forEach{ print($0) }