how do I sort a two dimensional array in the second dimension (comporator does not work because the-CodePudding

I have a string array, in the first dimension are letters, in the second numbers, I wanted to sort by the numbers in the second dimension, the problem is that I have problems because the same number occurs several times, in the numbers that do not occur twice, it is sorted correctly, from the moment where a double number occurs, not.At least I have with a comporator the problen

I tried this, to sort, with this comparator method:

public static void main(String[] args) {
    String[][] test = new String[5][2];
    test[0][0] = "a";
    test[1][0] = "a";
    test[2][0] = "a";
    test[3][0] = "a";
    test[4][0] = "a";
    test[0][1] = "1";
    test[1][1] = "2";
    test[2][1] = "1";
    test[3][1] = "3";
    test[4][1] = "4";
    Comparator<String[]> test2 = new Comparator<String[]>() {

        @Override
        public int compare(String[] o1, String[] o2) {
            if (Integer.parseInt(o1[1]) > Integer.parseInt(o1[1])) {
                return 1;
            } else if (Integer.parseInt(o1[1]) < Integer.parseInt(o1[1])) {
                return -1;
            } else {
                return 0;
            }
        }

    };

    Arrays.sort(test, test2);

    for (String[] t : test) {
        System.out.println(t[1]);
    }

}

The output is:

Same numbers makes problems... With out a same number correctly

4 would be the output...

(correct output from the example needed to be:

)

CodePudding user response：

This yields the correct output:

        String[][] sorted = Arrays.stream(test)
                .sorted(Comparator.comparingInt(a -> Integer.parseInt(a[1])))
                .toArray(String[][]::new);

How it works should be pretty self explanatory, if something is unclear let me know and i can clarify.

If u just want to modify the existing array then:

Arrays.sort(test, Comparator.comparingInt(a -> Integer.parseInt(a[1])));

The issue in ur existing code was that u weren't using o2, so the comparisons didn't really make any sense.

The working version would be be:

        Comparator<String[]> test2 = new Comparator<String[]>() {

            @Override
            public int compare(String[] o1, String[] o2) {
                if (Integer.parseInt(o1[1]) > Integer.parseInt(o2[1])) {
                    return 1;
                } else if (Integer.parseInt(o1[1]) < Integer.parseInt(o2[1])) {
                    return -1;
                } else {
                    return 0;
                }
            }
        };

Which is equivalent to:

        Comparator<String[]> test2 = (o1, o2) -> {
            return Integer.compare(Integer.parseInt(o1[1]), Integer.parseInt(o2[1]));
        };

Simplified even more:

Comparator<String[]> test2 = Comparator.comparingInt(o -> Integer.parseInt(o[1]));