Equivalent functionality of Matlab sortrows() in MathNET.Numerics?

Question

Is there a MathNET.Numerics equivalent of Matlab’s sortrows(A, column), where A is a Matrix<double>?

To recall Matlab's documentation:

B = sortrows(A,column) sorts A based on the columns specified in the vector column. For example, sortrows(A,4) sorts the rows of A in ascending order based on the elements in the fourth column. sortrows(A,[4 6]) first sorts the rows of A based on the elements in the fourth column, then based on the elements in the sixth column to break ties.

Answer 1

Similar to my answer to your other question, there's nothing inbuilt but you could use Linq's OrderBy() method on an Enumerable of the matrix's rows. Given a Matrix<double> x,

x.EnumerateRows() returns an Enumerable<Vector<double>> of the matrix's rows. You can then sort this enumerable by the first element of each row (if that's what you want).

In C#,

var y = Matrix<double>.Build.DenseOfRows(x.EnumerateRows().OrderBy(row => row[0]));

Example

Writing this as an extension method:

public static Matrix<double> SortRows(this Matrix<double> x, int sortByColumn = 0, bool desc = false) {
    if (desc)
        return Matrix<double>.Build.DenseOfRows(x.EnumerateRows().OrderByDescending(row => row[sortByColumn]));
    else
        return Matrix<double>.Build.DenseOfRows(x.EnumerateRows().OrderBy(row => row[sortByColumn]));
}

which you can then call like so:

var y = x.SortRows(0); // Sort by first column

Here's a big fiddle containing everything