How to construct an n-dimensional array from data

What you're describing is a matrix. That's not the same thing as an array of arrays. For example, the following is a legal [[Int]], but is an illegal Matrix2:

[[1, 2], [1]]

Swift doesn't have a built-in matrix type. You have to build your own. There are a lot of small projects out there to look for inspiration. I don't know if any are really baked enough to consider full implementations, but they're good enough to get you on the right track. They often want to include Accelerate, which greatly increases the complexity if you don't need it.

• https://github.com/hollance/Matrix
• https://github.com/stsievert/swix

The heart of any Matrix type, if you want to build your own, is something like this:

struct Matrix {
    private var storage: [Int]
    let rows: Int
    let columns: Int

    init(rows: Int, columns: Int) {

        precondition(rows > 0 && columns > 0)

        self.rows = rows
        self.columns = columns
        self.storage = Array(repeating: 0, count: rows * columns)
    }

    subscript(row: Int, column: Int) -> Int {
        get {
            return storage[row * columns + column]
        }
        set {
            storage[row * columns + column] = newValue
        }
    }
}

The key point is that storage is just a flat array of elements, and you subscript into it by row and column.

One nice thing about this design is that your question falls out almost trivially, since your input is exactly the storage.

extension Matrix {
    enum Error: Swift.Error {
        case invalidShape
    }

    init(rowMajorValues: [Int], rows: Int, columns: Int) throws {
        self.init(rows: rows, columns: columns)
        guard storage.count == rowMajorValues.count else {
            throw Error.invalidShape
        }
        storage = rowMajorValues
    }
}