Remove duplicate arrays in a ArrayList?

Question

Is there a way to remove duplicates arrays in an ArrayList?
I tried to convert the ArrayList into a HashSet and back to remove the duplicate arrays.
But this won't work:

ArrayList<int[]> mylist = new ArrayList<int[]>(); 

mylist.add(new int[]{1,2});
mylist.add(new int[]{2,2}); // Duplicate
mylist.add(new int[]{2,2}); // Duplicate

Before:

{{1,2},{2,2},{2,2}}

After:

{{1,2},{2,2}}

extend ArrayList and override add/addAll methods by checking first if the new item already exists in the list — eldjon
– eldjon, Commented Jul 26, 2014 at 17:18
@xgeorgekx Ok, I gonna try this out using a hashCode based on the value (@laune ´s idea) — user3880174
– user3880174, Commented Jul 26, 2014 at 17:27

laune · Accepted Answer · 2014-07-26 17:06:32Z

2

Different array objects have different hashCode() values even if their contents are equal.

Offhand, I can't think of anything better than to wrap the arrays into a class and to hash all wrapped arrays using a hashCode based on the value and the Arrays.equals as an equals.

This would be O(n) as opposed to searching for duplicates in a nested loop (O(n^2)).

answered Jul 26, 2014 at 17:06

laune

31.3k3 gold badges32 silver badges44 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

user3880174 Over a year ago

I am gonna check with Arrays.equals a duplicate before adding it. Also thanks to @xgerogekx.

laune Over a year ago

Preventing the evil is alway best ;-) Although, it'll be costly and costlier with increasing list length.

Brett Okken · Accepted Answer · 2014-07-26 17:23:53Z

0

This cannot be done with an ArrayList, this could be done with a TreeSet and a custom Comparator implementation which is able to accurately compare the int[] objects.

For example:

public final class IntArrayComparator implements Comparator<int[]>
{
    public int compare(int[] a, int[] b)
    {
        if (a == null)
            return b == null ? 0 : 1;

        if (a.length != b.length)
            return a.length - b.length;

        for (int i=0; i<a.length; ++i)
        {
            final int diff = a[i] - b[i];
            if (diff != 0)
                return diff;
        }

        return 0;
    }
}

answered Jul 26, 2014 at 17:23

Brett Okken

6,3261 gold badge21 silver badges25 bronze badges

Collectives™ on Stack Overflow

Remove duplicate arrays in a ArrayList?

2 Answers 2

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related