How to call Parallel.ForEach with a multidimensional array

Question

I'm having a little trouble figuring out how to call the Parallel.ForEach with a 2D array of strings:

string[,] board = new string[,]{
        {"A", "B", "C", "D", "E" },
        {"F", "G", "H", "I", "J"},
        {"K", "L", "M", "N", "O"},
        {"0", "1", "2", "3", "4"}};

Parallel.ForEach(board, row =>
    {
        for (int i = 0; i < row.Length; ++i)
        {
            // find all valid sequences
        }
    });

If I don't specify the type explicitly I get the following error:

The type arguments for method 'System.Threading.Tasks.Parallel.ForEach(System.Collections.Generic.IEnumerable, System.Action)' cannot be inferred from the usage. Try specifying the type arguments explicitly.

What's the proper way to specify the type arguments explicitly?

Answer 1

The problem for you is that 2-dimensional arrays do not implement IEnumerable<one-dimensional-array>. (It does implement IEnumerable, but it's an IEnumerable of strings that "flattens" the array.) You can do two things:

• Change the string[,] to a jagged array-of-arrays, string[][].

• Implement your own extension method that iterates over a two-dimensional array and turns it into an IEnumerable<one-dimensional-array>.

Answer 2

You should still be able to make this work with a multi-dimensional array, just using Parallel.For instead of Parallel.ForEach:

string[,] board = new string[,] {
    {"A", "B", "C", "D", "E" },
    {"F", "G", "H", "I", "J"},
    {"K", "L", "M", "N", "O"},
    {"0", "1", "2", "3", "4"}
};

int height = board.GetLength(0);
int width = board.GetLength(1);

Parallel.For(0, height, y =>
    {
        for (int x = 0; x < width; ++x)
        {
            string value = board[y, x];
            // do whatever you need to do here
        }
    }
);