Getting a double[] row array of a double[,] rectangular array

Question

Suppose you have an array like:

double[,] rectArray = new double[10,3];

Now you want the fouth row as a double[] array of 3 elements without doing:

double[] fourthRow = new double[]{rectArray[3,0],
                                  rectArray[3,1], 
                                  rectArray[3,2]};

Is it possible someway? Even using a Marshal.Something approach?

Thanks!

Answer 1

You probably want to use a jagged array. That is not an array of 10 by 3 but instead an array of arrays.

Something like :

        double[][] rectArray;
         ....
        double [] rowArray = rectArray[3];

There are lots of places to learn more about jagged arrays. For example http://stackoverflow.com/questions/2458486/dynamically-created-jagged-rectangular-array

Answer 2

You can use Buffer.BlockCopy method:

const int d1 = 10;
const int d2 = 3;
const int doubleSize = 8;

double[,] rectArray = new double[d1, d2];
double[] target = new double[d2];

int rowToGet = 3;
Buffer.BlockCopy(rectArray, doubleSize * d2 * rowToGet, target, 0, doubleSize * d2);

Answer 3

If you must use a rectangular array and just want to simplify the syntax, you can use a method to get the row like so:

double[] fourthRow = GetRow(rectArray, 3);

public static T[] GetRow<T>(T[,] matrix, int row)
{
    var columns = matrix.GetLength(1);
    var array = new T[columns];
    for (int i = 0; i < columns; ++i)
        array[i] = matrix[row, i];
    return array;
}

Answer 4

LINQ to the rescue:

var s = rectArray.Cast<double>().Skip(9).Take(3).ToArray();

Explanation: Casting a multi-dimensional array flattens it to a single-dimensional array. After that all we need to do is skip to the element we want (the 4th element in the 2-D array resolves to Skip(9)...) and take 3 elements from it).