switching columns of a 2d array

so my problem is that i cannot get the elements of a 2d array to switch like i would be able to do in a single variable array. Ins开发者_JS百科tead of switching the elements they are just being continuously rewritten...

for (int column = 0; column < m[0].length; column++) {
    shufcol = (int)(Math.random()*4);
    temp = column;
    System.out.println(shufcol);

    for(int row = 0; row < m.length; row++) {
        temp = row;
        m[row][temp]=m[row][column];
        m[row][column]= m[row][shufcol];
        m[row][temp] = m[row][shufcol];
    }
}

input array (3X4) {{0 1 2 3} {1 4 5 6} {0 7 8 9}}

output array {{2 2 3 2} {5 5 6 5} {8 8 9 8}}

If your curious about the math.random, that is just to generate a random column between 0 to 3 to switch with. Again the issue is why is it only rewriting elements and not switching them?

---

I don't fully understand what you want to achieve at the end (because you haven't told), but I think, if you reread this piece of code:

temp = row;
m[row][temp]=m[row][column];
m[row][column]= m[row][shufcol];
m[row][temp] = m[row][shufcol];

several times and try to execute it with piece of paper and pen you'll find the mistake.

---

If I understood, this will switch the values in column and shufcol for all rows (I didn't test it):

for (int column = 0; column < m[0].length; column++) {
    shufcol = (int)(Math.random()*4);
    System.out.println(shufcol);

    for(int row = 0; row < m.length; row++) {
        temp = m[row][shufcol];
        m[row][shufcol] = m[row][column];
        m[row][column] = temp;
    }
}

---

This will switch elements inside their rows:

    //input array (3X4) {{0 1 2 3} {1 4 5 6} {0 7 8 9}}
    int[][] m = {{0, 1, 2, 3}, {1, 4, 5, 6}, {0, 7, 8, 9}};


    for (int column = 0; column < m[0].length; column++) {
        int shufcol = (int)(Math.random()*4);
        int shufrow = (int)(Math.random()*3); //need row to switch with, too
        for(int row = 0; row < m.length; row++) {
            if(row == shufrow){
                int tempField =m[row][column];
                m[row][column]= m[row][shufcol];
                m[row][shufcol] = tempField;
                System.out.println("In row " + row + " : column " + column + " was switched with column " + shufcol + "!");
                break; //just switch once per row, easier debugging ^^-d
            }
        }
    }

    //print output array
    for(int row = 0; row < m.length; row++) {
        String line = "\n";
        for (int column = 0; column < m[0].length; column++) {
            line += m[row][column] + " ";
        }
        System.out.print(line);
    }

Output:

In row 2 : column 0 was switched with column 2!
In row 0 : column 1 was switched with column 2!
In row 1 : column 2 was switched with column 3!
In row 0 : column 3 was switched with column 2!

0 2 3 1 
1 4 6 5 
8 7 0 9 

Since i am not totally sure what you want to do, here is switching elements in the whole array randomly:

    //input array (3X4) {{0 1 2 3} {1 4 5 6} {0 7 8 9}}
    int[][] m = {{0, 1, 2, 3}, {1, 4, 5, 6}, {0, 7, 8, 9}};

    for (int column = 0; column < m[0].length; column++) {
        int shufcol = (int)(Math.random()*4);
        int shufrow = (int)(Math.random()*3); //need row to switch with, too
        //there is no point in duplicating the count variable of a loop!
        System.out.println(shufcol);

        for(int row = 0; row < m.length; row++) {
            //check that random field is not current field!
            if(row != shufrow && column != shufcol){
                //switch current with random
                int temp = m[row][column]; // le backuppe
                m[row][column] = m[shufrow][shufcol]; // write le new value of "random source field" to current field
                m[shufrow][shufcol] = temp; // write value of current field to "random source field"
                System.out.println("switched [" + row + "][" + column + "] with [" + shufrow + "]["+ shufcol + "]");
                break; // use break to switch only once per row, easier debugging ^^-d
            }
            else {
                System.out.println("will not switch with self!");
            }

        }
    }

    //print output array
    for(int row = 0; row < m.length; row++) {
        String line = "\n";
        for (int column = 0; column < m[0].length; column++) {
            line += m[row][column] + " ";
        }
        System.out.print(line);
    }

Yielding the following output:

2
switched [0][0] with [2][2]
0
switched [0][1] with [1][0]
0
switched [0][2] with [2][0]
2
switched [0][3] with [1][2]

8 1 0 5 
1 4 3 6 
2 7 0 9 

Hope this helps! ^^-d