n-dimensional Array

Question

I want to create an n-dimensional array of doubles. At compile-time, the number of dimensions n is not known.

I ended up defining the array as a dictionary, with the key being an array of ints corresponding to the different axes (so in a 3-dimensional array, I'd supply [5, 2, 3] to get the double at (5, 2, 3) in the array.

However, I also need to populate the dictionary with doubles from (0, 0, ... 0) to (m1, m2, ... mn), where m1 to mn is the length of each axis.

My initial idea was to create nested for-loops, but as I still don't know how many I'd need (1 for each dimension), I can't do this at compile-time.

I hope I've formulated the question in an understandable manner, but feel free to ask me to elaborate parts.

Answer 1

To create a n-dimensional array, you can use the Array.CreateInstance method:

Array array = Array.CreateInstance(typeof(double), 5, 3, 2, 8, 7, 32));

array.SetValue(0.5d, 0, 0, 0, 0, 0, 0);
double val1 = (double)array.GetValue(0, 0, 0, 0, 0, 0);

array.SetValue(1.5d, 1, 2, 1, 6, 0, 30);
double val2 = (double)array.GetValue(1, 2, 1, 6, 0, 30);

To populate the arrays, you can use the Rank property and GetLength method to return the length of the current dimension, using a couple of nested for loops to do a O(n^m) algo (warning - untested):

private bool Increment(Array array, int[] idxs, int dim) {
    if (dim >= array.Rank) return false;

    if (++idxs[idxs.Length-dim-1] == array.GetLength(dim)) {
        idxs[idxs.Length-dim-1] = 0;
        return Increment(array, idxs, dim+1);
    }
    return true;
}

Array array = Array.CreateInstance(typeof(double), ...);
int[] idxs = new int[array.Rank];
while (Increment(array, idxs, 0)) {
    array.SetValue(1d, idxs);
}