How can I remove duplicates from an array list using two methods?

Question

The first method finds the duplicate and the second removes it. I tried the following code and it does not work. I don't understand why. to be done using two methods. When I call the methods, they do not remove the duplicates. The arraylist is unchanged. I want to remove the duplicates using two methods.

public static int find(ArrayList<String> s, int i) {

    for (int j = i + 1; j < s.size(); j = j + 1) {
        if (s.get(i) == s.get(j)) {
            return j;
        }
    }

    return -1;
}


public static void removeDuplicates(ArrayList<String> s) {
    for (int i = 0; i < s.size(); i = i + 1) {
        int foundAt = (find(s, i));
        if (foundAt >= 0) {
            s.remove(i);
        }
    }
}

Instead of `s.get(i) == s.get(j)` use `s.get(i).equals(s.get(j))` — BadIdeaException, Mar 27 '14 at 18:17

score 1 · Answer 1 · answered Mar 27 '14 at 18:17

1

Don't be bothered:

public static List<String> removeDups(final List<String> orig)
{
    return new ArrayList<>(new LinkedHashSet<>(orig));
}

(note the use of LinkedHashSet, we want to preserve element iteration ordering)

answered Mar 27 '14 at 18:17

fge

119,121
33
254
329

score 0 · Answer 2 · answered Mar 27 '14 at 18:17

Why don't you simply dump it in a Set

List<String> listduplicates =  new ArrayList<String>(10);
//add elements to the list
Set<String> as = new HashSet<String>(listduplicates );

List<String> listunique =  new ArrayList<String>(as.size());

listunique now give unique elements

Raul Guiu · Answer 3 · 2014-03-27T18:36:03.703

If you want to do it with two methods, and following your same idea, you could fix your methods to be:

   public static int find(List<String> s, int j) {
        for(int i=j;i<s.size();i++) {
            if (s.lastIndexOf(s.get(i)) != i)  {
                return i;
            }
        }
        return -1;
    }


    public static void removeDuplicates(ArrayList<String> s) {
        for (int j=0; j<s.size();j++) {
            int i = -1;
            while((i=find(s,j))>=0) {
                s.remove(i);
            }
        }
    }

score 0 · Answer 4 · answered Mar 27 '14 at 18:22

If you are using Java 8 you can use the Stream API with the distinct() operation to eleminate duplicates:

List<Integer> list = Arrays.asList(5, 3, 6, 5, 4, 6);
List<Integer> filtered = list.stream().distinct().collect(Collectors.toList());
System.out.println("filtered: " + filtered); // [5, 3, 6, 4]

score 0 · Answer 5 · answered Mar 27 '14 at 18:28

I have checked your code and it runs fine and removes duplictaes from the list. You may change removeDuplicates method to remove duplicates that come later in the list.

 public static void removeDuplicates(ArrayList<String> s) {
            for (int i = 0; i < s.size(); i = i + 1) {
                int foundAt = (find(s, i));
                if (foundAt >= 0) {
                    s.remove(foundAt);
                }
            }
        }

How can I remove duplicates from an array list using two methods?

5 Answers5