How to print a RealMatrix with table formating

Question

I'm using apache-commons-math RealMatrix on my project to handle matrix operations, however I can't print it with proper formatting.

For every matrix i have so far it goes like this:

double coord[][] = new double[3][3];
                    
        coord[0][0] = 1d;    
        coord[0][1] = 0d;    
        coord[0][2] = 0d;    

        coord[1][0] = 2d;    
        coord[1][1] = 1d;    
        coord[1][2] = 1d;    

        coord[2][0] = 3d;    
        coord[2][1] = 2d;    
        coord[2][2] = 0d;    
    
        
    System.out.println("coordinates  [nó, x, y]");
        for(int co = 0 ; co < 3 ; co++){
            for(int or = 0 ; or < 3 ; or++){
                System.out.printf("%10.5f\t",coord[co][or]);
            }
            System.out.print("\n");
        }

outputing:

    coordinates  [nó, x, y]
   1,00000     0,00000     0,00000  
   2,00000     1,00000     1,00000  
   3,00000     2,00000     0,00000

But when i'm using RealMatrix to print, it only prints in string (as far as i could find by myself) like this:

double coord[][] = new double[3][3];
                            
            coord[0][0] = 1d;    
            coord[0][1] = 0d;    
            coord[0][2] = 0d;    

            coord[1][0] = 2d;    
            coord[1][1] = 1d;    
            coord[1][2] = 1d;    

            coord[2][0] = 3d;    
            coord[2][1] = 2d;    
            coord[2][2] = 0d;   
        
        
        RealMatrix m = MatrixUtils.createRealMatrix(coord);                  
        System.out.println(m.toString());
        

outputing:

Array2DRowRealMatrix{{1.0,0.0,0.0},{2.0,1.0,1.0},{3.0,2.0,0.0}}

How can I get the same output as in the first case using RealMatrix? From the error messages I get when I try to do it by myself, it seems that if I can convert the realmatrix back to an array it would solve my problem, but I cant manage to do that either...

Edit 1: As I'm trying to solve this, I found that getting the results of my matrix operations in an array would be very helpful, or at least a way of reading specific values out of them.

Edit 2: Added Java tag

Flummery

Good idea to add a language tag as a general rule. – Terpsichore

Answer 1

Apache's commons-math has a facility for formatting matrices to strings, it is in RealMatrixFormat . Here is a simple example that will generate a table like output:

import org.apache.commons.math3.linear.MatrixUtils;
import org.apache.commons.math3.linear.RealMatrix;
import org.apache.commons.math3.linear.RealMatrixFormat;

public class Main {
    public static void main(String[] args) {


        double data[][] = new double[2][3];
        data[0][0] = 11;
        data[0][1] = 12;
        data[0][2] = 13;

        data[1][0] = 21;
        data[1][1] = 22;
        data[1][2] = 23;

        RealMatrix matrix = MatrixUtils.createRealMatrix(data);

        RealMatrixFormat matrixFormat = new RealMatrixFormat("", "", "", "\n", "", ", ");
        System.out.println(matrixFormat.format(matrix));
    }
}

produces:

11, 12, 13
21, 22, 23

Concuss

I suggest to give a java example instead as the question is tagged with java. – Karlise

Answer 2

You can get the underlying data as a 2-dimensional array using getData. Implementations will in general return a copy of the data from this method. Some implementations expose a getDataRef method which returns a reference to the underlying data itself. Using one of these, you can format the data however you like.

Boulevardier