Create matrix from array with Math.Net

Question

I've a list made by sublists of numbers. This is named biglist and it is:

biglist[0] = { 1, 2, 3, 4, 5 };
biglist[1] = { 5, 3, 3, 2, 1 };
biglist[2] = { 3, 4, 4, 5, 2 };

Now I want to create a matrix using these sublists where each sublist represents a column of the matrix. My final result has to be a matrix 5x3 in this way:

1 | 5 | 3   
---------
2 | 3 | 4   
---------  
3 | 3 | 4   
---------  
4 | 2 | 5   
---------  
5 | 1 | 2

I know how to convert a list to array but I don't know how to assemble these arrays to create the matrix.

I think the package Math.Net could work for my purpose, but I don't understand how it's possible to do this with it.

CSDev · Accepted Answer · 2019-07-21T13:12:59.107

2

MathNet limitation is you can use only Double, Single, Complex or Complex32 numeric types for that purpose.

using MathNet.Numerics.LinearAlgebra;

// ...

double[][] biglist = new double[3][];

biglist[0] = new double[] { 1, 2, 3, 4, 5 };
biglist[1] = new double[] { 5, 3, 3, 2, 1 };
biglist[2] = new double[] { 3, 4, 4, 5, 2 };

Matrix<double> matrix = Matrix<double>.Build.DenseOfColumns(biglist);
Console.WriteLine(matrix);

Gives:

DenseMatrix 5x3-Double
1  5  3
2  3  4
3  3  4
4  2  5
5  1  2

edited Jul 21 '19 at 13:12

answered Jul 21 '19 at 12:23

CSDev

3,177
6
19
37

Thank you! What if I had lists of sublists? I mean If I had biglist made by biglist[0] and biglist[1] where biglist[0] is made up of biglist[0][0]=array1, biglist[0][1]=array2, biglist[1][0]=array3, biglist[1][1]=array4 and I would like to create two matrices, one with biglist[0] and the other with biglist[1]? Is there the chance to use for loop and Add with Math.Net? – Roberto Ruggeri Jul 21 '19 at 14:58
@Roberto Ruggeri, you are welcome! Yes, it's possible. Btw, here, on stackoverflow we express our attitude by voting. E.g., I found your question interesting, so I upvoted it. If my answer seem helpful to you, you can upvote it too. If the answer solves your problem (and it appears to), you can accept it. – CSDev Jul 21 '19 at 16:36
Hi @Alex sorry but I'm new here therefore I'm just learning everything :) I upvoted your answer too now! Could you please tell me how it is possible to do what I asked? – Roberto Ruggeri Jul 21 '19 at 16:40
@Roberto Ruggeri, that's OK! In your case you can just have `var matrix1 = Matrix.Build.DenseOfColumns(biglist[0])` and `var matrix2 = Matrix.Build.DenseOfColumns(biglist[1])`. Or you can populate a collection dynamically with `for-loop` and `Add` and then pass it to `DenseOfColumns(...)`. – CSDev Jul 21 '19 at 16:57
How can I populate a collection dynamically?? I don't want to create matrix1 and matrix 2 but only matrix which stores matrix[1] and matrix[2] as we do with Lists. – Roberto Ruggeri Jul 21 '19 at 17:02
You can have `Matrix[]`. As far as I know `MathNet` does not deal with matrices of matrices. – CSDev Jul 21 '19 at 20:50
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/196812/discussion-between-alex-and-roberto-ruggeri). – CSDev Jul 22 '19 at 13:24

Shehab · Answer 2 · 2019-07-21T12:05:20.710

If I understand you very well you are trying to do something like this :

    public static int[,] GetMatrix(IReadOnlyList<int[]> bigList)
    {
        if (bigList.Count == 0) throw new ArgumentException("Value cannot be an empty collection.", nameof(bigList));

        var matrix = new int[bigList.Count, bigList[0].Length];

        for (var bigListIndex = 0; bigListIndex < bigList.Count; bigListIndex++)
        {
            int[] list = bigList[bigListIndex];

            for (var numberIndex = 0; numberIndex < list.Length; numberIndex++) matrix[bigListIndex, numberIndex] = list[numberIndex];
        }

        return matrix;
    }

    private static void Main(string[] args)
    {
        var biglist = new List<int[]>
        {
            new[] {1, 2, 3, 4, 5},
            new[] {5, 3, 3, 2, 1},
            new[] {3, 4, 4, 5, 2}
        };

        int[,] matrix = GetMatrix(biglist);

        for (var i = 0; i < matrix.GetLength(1); i++)
        {
            for (var j = 0; j < matrix.GetLength(0); j++)
                Console.Write($" {matrix[j, i]} ");
            Console.WriteLine();
        }


        Console.ReadKey();
    }

Create matrix from array with Math.Net

2 Answers2