Converting 2D integer array to String

Question

I made a 2D array containing integer values and want to convert it into a string, but I'm really confused on what I'm able to put into //something to get the output I want.

public static void main(String[] args) {
    final int [][] test = { {1, 6, 11, 16, 21}, 
                            {2, 7, 12, 17, 22}, 
                            {3, 8, 13, 18, 23}, 
                            {4, 9, 14, 19, 24}, 
                            {5, 10, 15, 20, 25} };
    System.out.println(TwoDOneD.DownNUp(test));

public static String DownNUp(int [][] test) {
    String res = "";
    for (int r = 0; r < test[0].length; r++) {
         for (int c = 0; c < test.length; c++) {
            if (c % 2 == 1) {
                //something
            } else {
                res += test[c][r] + " ";
            }
        }
    }
    return res;
}

The output I'm trying to get is why I have (c % 2 == 1); in every odd column, it's supposed to go down, and in every even column, it goes right back up.

1 2 3 4 5 10 9 8 7 6 11 12 13 14 15 20 19 18 17 16 21 22 23 24 25

It's in every odd column because it seems that c%2 == 0 is doing nothing in the if block. If you want to convert entire array to string, why have the check? — Sid
– Sid, Commented Nov 10, 2018 at 4:34
@Sid That's because there's nothing but a comment in the c%2 == 1, which is where I would put the actual code. And I want the entire array to be converted into a string in that format. — Excel
– Excel, Commented Nov 10, 2018 at 4:39

c0der · Accepted Answer · 2018-11-10 04:46:46Z

5

You need to change iteration direction, based on c % 2 == 0

public static void main(String[] args) {

    final int [][] test = { {1, 6, 11, 16, 21}, 
            {2, 7, 12, 17, 22}, 
            {3, 8, 13, 18, 23}, 
            {4, 9, 14, 19, 24}, 
            {5, 10, 15, 20, 25} };
    System.out.println(downUp(test));
}

public static String downUp(int [][] test) {
    String res = "";
    for (int c = 0; c < test[0].length; c++) {

        if (c % 2 == 0) {
            for (int r = 0; r < test.length; r++) {
                res += test[r][c] + " ";
            }

        } else {

            for (int r = test.length -1 ; r >=0 ; r--) {
                res += test[r][c] + " ";
            }
        }
    }
    return res;
}

A side note: it would be better implemented using a StringBuilder like so:

public static String downUp(int [][] test) {

    StringBuilder res = new StringBuilder();

    for (int c = 0; c < test[0].length; c++) {

        if (c % 2 == 0) {
            for (int r = 0; r < test.length; r++) {
                res.append(test[r][c]).append(" ");
            }

        } else {

            for (int r = test.length -1 ; r >=0 ; r--) {
                res.append(test[r][c]).append(" ");
            }
        }
    }
    return res.toString();
}

edited Nov 10, 2018 at 4:46

answered Nov 10, 2018 at 4:41

c0der

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4 Comments

Excel Over a year ago

Worked perfectly. I'll be sure to keep in mind that when I want to change the direction that I'm running to change the iteration.

Sid Over a year ago

@Excel Also view other answers before accepting an answer. There may be better ways of achieving this. Just saying.

Excel Over a year ago

@Sid I'll be sure to look for more efficient ways that I can understand at the level I'm at in my coding, thanks :)

c0der Over a year ago

I agree with @Sid. What I posted is aimed at making the change of iteration direction clear and simple. There are other, more concise ways to do so like saeedata proposed

saeedata · Accepted Answer · 2018-11-10 04:42:58Z

1

i think this is that you want:

public static String DownNUp(int[][] test) {
        String res = "";
        for (int r = 0; r < test[0].length; r++) {
            for (int c = 0; c < test.length; c++) {

                if (r % 2 != 0) {
                    res += test[test.length - 1 - c][r] + " ";
                } else {
                    res += test[c][r] + " ";
                }
            }
        }
        return res;
    }

answered Nov 10, 2018 at 4:42

saeedata

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1 Comment

c0der Over a year ago

+1 . I think naming could be better if you changed r (which represents column) to c and c to r. Also for method name use downUp.

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