Question

I have an [] that has some numbers (distances from some point).
I want to create an array of indexes into the first array where the indexes are sorted by the distance.

e.g.

suppose double[] dist=new double[5] {3.2, 1.4, 7.3, 2.2, 9.1};
then I want to get an array like this:

int[] sortedIndexes=new int[5] {1, 3, 0, 2, 4};

so if I want the second nearest distance I can check dist[sortedIndexes[1]].
I don’t want to sort the original array, just the array of indexes based on the distances.

UPDATE 1:
The Code I was trying looks like this:

Collections.sort(sortedIDXs, new Comparator<Integer>() {
    public int compare(int idx1, int idx2) {
        return Double.compare(distances[idx1], distances[idx2]);
    }
});

But I am getting several errors with it with the most “problematic” one being:
“Cannot refer to a non-final variable distances inside an inner class defined in a different method“

Thanks

Answer 1

You’re on the right track, but

• You’re better off with an Integer array than an int array if you’re using a generic Comparator<Integer>.
• You have to use Arrays.sort instead Collections.sort for sorting an array.

• You have to make the distances variable final if it’s referenced in an anonymous inner class.

  final double[] distances=new double[]{3.2, 1.4, 7.3, 2.2, 9.1};
  Integer[] sortedIDXs  = new Integer[]{0,1,2,3,4};
  Arrays.sort(sortedIDXs, new Comparator<Integer>() {
      public int compare(Integer idx1, Integer idx2) {
          return Double.compare(distances[idx1], distances[idx2]);
      }
  });