Arrays.sort for 2-D Integer Array failing

Question

I'm using the below method to sort a 2D Integer array. But there seems to be some issue with the sorting. Can someone please help.

private static Integer[][] sort(Integer[][] bs) {

    Arrays.sort(bs, new Comparator<Integer[]>() {
        @Override
        public int compare(Integer[] int1, Integer[] int2) {
            Integer numOfKeys1 = int1[1];
            Integer numOfKeys2 = int2[1];
            return numOfKeys1.compareTo(numOfKeys2);
        }
    });

    return bs;
  }

Input Array:

480 615
1320 1395
1020 1140
420 585
540 780
960 1065
720 810
690 750

Output:

420 585
480 615
690 750
540 780 - not sorted
720 810
960 1065
1020 1140
1320 1395

OnABauer · Accepted Answer · 2013-08-06 12:10:46Z

1

You're sorting by the second value not the first. Try something like:

Integer numOfKeys1 = int1[0];
Integer numOfKeys2 = int2[0];

answered Aug 6, 2013 at 12:10

OnABauer

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Comments

Danstahr · Accepted Answer · 2013-08-06 12:35:35Z

1

It actually IS sorted, but the key is the second record in your array. To sort it by the first node, you need to change your comparator to

public int compare(Integer[] int1, Integer[] int2) {
    Integer numOfKeys1 = int1[0];
    Integer numOfKeys2 = int2[0];
    return numOfKeys1.compareTo(numOfKeys2);
}

Or better write a comparator that sorts lexicographically

public int compare(Integer[] int1, Integer[] int2) {            
    int minlen = Math.min(int1.length, int2.length);
    for (int i = 0; i < minlen; ++i) {
        int cmp = int1[i].compareTo(int2[i]);
        if (cmp != 0) {
            return cmp;
        }
    }
    // so far the arrays are same, the shorter goes first
    return int1.length - int2.length;
}

edited Aug 6, 2013 at 12:35

answered Aug 6, 2013 at 12:19

Danstahr

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