Java Matrices - Transpose & Sum

Question

I am working on a Matrix program on eclipse and I am currently stuck on 2 methods in which I thought were the most simplest of all. The first method that I am working on is to take the sum of 2 different 2D arrays from the @Test cases and returning the sum in a new 2D array. I already have an 2D array instance variable. The reason I am stuck is because the of the parameter in the method. The parameter doesn't give any variable other than the class (Matrix) and the variable (other). So I was wondering how to go about getting this method started and most importantly returning the sum array.

The other method I am stuck on is the transpose method where you must flip the rows and columns of the given 2D array. I know I must create a temp 2D array in order to store the content back into the original 2D array but for some reason it is not passing the test cases. If someone could please help me with these two methods, it would be much appreciated.

import java.util.Arrays;

public class Matrix {

    private int[][] array;
    private int[][] array2;
    private int theRow;
    private int theCol;

    public Matrix(int[][] arrayOfArrays) {
        // TODO Auto-generated constructor stub
        array = new int[arrayOfArrays.length][arrayOfArrays[0].length];

        for (int r = 0; r < arrayOfArrays.length; r++) {
            for (int c = 0; c < arrayOfArrays[r].length; c++) {
                array[r][c] = arrayOfArrays[r][c];
            }
        }

    }

    public int get(int row, int column) {

        return array[row][column];
    }


    public int getNumberOfRows() {

    int nRows = array.length;

    return nRows;
    }


    public int getNumberOfColumns() {

    int nCols = array[0].length;

    return nCols;


    }
    public String toString() {
        String res = "";
        for (int r = 0; r < array.length; r++) {
            for (int c = 0; c < array[r].length; c++) 
                res = res + array[r][c];
        }

        return res;
    }
    public Matrix sum(Matrix other) {


        return sum;
    }
    public void scalarMultiply(int scalar) {

        for (int r = 0; r < array.length; r++)  {
            for (int c = 0; c < array[0].length; c++) {
                array[r][c] = array[r][c] * scalar;
            }
        }
    }

    public void transpose() {

        int m = array.length;
        int n = array[0].length;

        int[][] transpose = new int [n][m];

        int temp;
        for (int r = 0; r < m; r++)  {
            for (int c = 0; c < n; c++)  {
                transpose[c][r] = array[r][c];
                array[r][c] = array[c][r];
                array[c][r] = transpose[c][r];                      
            }
        }
    }

    //The test cases for sum method and transpose method

    @Test
    public void testSum() {
        int[][] a1 = { { 1, 2, 3 }, 
                       { 5, 6, 7 } };
        Matrix a = new Matrix(a1);

        int[][] a2 = { { -2, -2, -2 }, 
                       { 4, 4, 4 } };
        Matrix b = new Matrix(a2);

        Matrix c = a.sum(b);

        assertEquals(-1, c.get(0, 0));
        assertEquals(0, c.get(0, 1));
        assertEquals(1, c.get(0, 2));
        assertEquals(9, c.get(1, 0));
        assertEquals(10, c.get(1, 1));
        assertEquals(11, c.get(1, 2));
    }

    @Test
    public void testTranspose() {

        int[][] a1 = { { 1, 3, 5 },
                       { 2, 4, 6 } };
        Matrix a = new Matrix(a1);
        a.transpose();

        assertEquals(1, a.get(0, 0));
        assertEquals(2, a.get(0, 1));
        assertEquals(3, a.get(1, 0));
        assertEquals(4, a.get(1, 1));
        assertEquals(5, a.get(2, 0));
        assertEquals(6, a.get(2, 1));
    }

Answer 1

You need change the dimensions, for example, 2x3 -> 3x2.

import java.util.Arrays;

public class Matrix {

    private int[][] array;
    private int[][] array2;// remove this
    private int theRow;// remove this
    private int theCol;// remove this


    public void transpose() {

        int m = array.length;
        int n = array[0].length;

        int[][] transpose = new int [n][m];

        for (int r = 0; r < m; r++)  {
            for (int c = 0; c < n; c++)  {
                transpose[c][r] = array[r][c];                     
            }
        }
        array = transpose;
    }
}