CODEWITHSUNDEEP
c#math.net
elina
elina

Reputation: 21

Mathnet numerics indexing parts of a matrix

Using Math.Net Numerics, how can I index parts of a matrix?

For example, I have a collection of ints and I want to get a submatrix with the rows and columns chosen accordingly.

A[2:3,2:3] should give me that 2 x 2 submatrix of A where the row index and the column index is either 2 or 3

Upvotes: 2

Views: 3238

Answers (2)

gwizardry
gwizardry

Reputation: 511

I suspect you were looking for something like this Extension method. 

public static Matrix<double> Sub(this Matrix<double> m, int[] rows, int[] columns)
{
    var output = Matrix<double>.Build.Dense(rows.Length, columns.Length);
    for (int i = 0; i < rows.Length; i++)
    {
        for (int j = 0; j < columns.Length; j++)
        {
            output[i,j] = m[rows[i],columns[j]];
        }
    }

    return output;
}

I've omitted the exception handling to ensure rows and columns are not null.

Upvotes: 0

MoonKnight
MoonKnight

Reputation: 23833

Just use some thing like 

var m = Matrix<double>.Build.Dense(6,4,(i,j) => 10*i + j);
m.Column(2); // [2,12,22,32,42,52]

to access the desired column use the Vector<double> Column(int columnIndex) extension method.

Upvotes: 2

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