array-transposed.swift

extension Array where Element: Collection {
    // Calculates the size of a matrix.
    func size() -> (cols: Int, rows: Int) {
        let numRows = self.count
        let numCols = self.reduce(0, { Swift.max($0, $1.count) })
        return (numCols, numRows)
    }

    // Transposes a matrix.
    //
    // For example:
    //
    // let m = [[1, 2], [4, 5, 6]]
    // print(m.transposed(with: -1)) // outputs: [[1, 4], [2, 5], [-1, 6]]
    // 
    // let m = [["a", "b", "c"], ["d", "e"]]
    // print(m.transposed(with: " ")) // outputs: [["a", "d"], ["b", "e"], ["c", " "]]
    func transposed(with char: Element.Element) -> [[Element.Element]] {
        let (numCols, numRows) = self.size()
        var result = (0..<numCols).map { _ in (0..<numRows).map {_ in char } }
        for (i, row) in self.enumerated() {
            for (j, cell) in row.enumerated() {
                result[j][i] = cell
            }
        }
        return result
    }
}