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 do
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 Dynamically created jagged rectangular array