Sorting a ArrayList on two attributes within the float array

Question

I am making use of the following ArrayList: ArrayList<float[]> notes = new ArrayList<float[]>();

I managed to perform the sorting on the first element of the float[] array without any problem. Now I am also trying to sort the ArrayList on using a second attributes. However I cannot manage to sort the list again on the second element of the float arrays ie. float[1].

Any hints?

what do you mean? `float[]` is an array of primitive `float`s (not Objects) — blurfus, Apr 07 '15 at 23:43
Hint http://stackoverflow.com/questions/369512/how-to-compare-objects-by-multiple-fields/369867#369867 — Steve Kuo, Apr 07 '15 at 23:48
@ryekayo He is trying to sort the List that contains arrays not the arrays in each list, so you need to use Collections.sort not Arrays.sort — Sean F, Apr 08 '15 at 03:53

Sean F · Answer 1 · 2015-04-08T03:42:42.147

You can use Collections.sort to sort the array and then use your own Comparator to specify how you want to sort the values.

ArrayList<float[]> notes = new ArrayList<float[]>();
//adding some dummy data to the list
notes.add(new float[]{5f,6f,1f});
notes.add(new float[]{5f,2f,1f});
notes.add(new float[]{5f,1f,1f});

//Use Collections.sort to sort Ascending values on the second value in the float arrays
Collections.sort(notes, new Comparator<float[]>() {
    @Override
    public int compare(float[] o1, float[] o2) {
        if (o1[1] > o2[1]){
            return 1;
        }else if(o1[1] < o2[1]){
            return -1;
        }
        return 0;
    }
});

//Output the values
for (float[] f : notes){
    System.out.println(Arrays.toString(f));
}

Output:

[5.0, 1.0, 1.0]
[5.0, 2.0, 1.0]
[5.0, 6.0, 1.0]

Hint for simpler comparison: https://docs.oracle.com/javase/7/docs/api/java/lang/Float.html#compare%28float,%20float%29 — JB Nizet, Apr 08 '15 at 07:46

Sorting a ArrayList on two attributes within the float array

1 Answers1