Remove duplicates from a list in an Arraylist in java

Question

I checked many examples but i could not applied for my variables. I have a ArratyList Of lists of Strings.

ArrayList<List<String>> bulkUploadList = new ArrayList<List<String>>();

and it's look like this:

[id, title, tags, descriptions]

[4291483113.0000000000000, Camden, camdentown;london, NoValue]
[4292220054.0000000000000, IMG_2720, NoValue, NoValue]
[4292223824.0000000000000, IMG_2917, london;camdentown, NoValue]
[4292224728.0000000000000, IMG_2945, London;CamdenTown, NoValue]

I want to remove those rows which have the same titles and the same tags. I do not know how work with HashSet since I have a ArrayList of List of Strings.

Why you have an arraylist of strings in the first place ? Create a class to hold this datas. — Alexis C.
– Alexis C., Commented Dec 10, 2015 at 12:50
Would you please explain more, what do you mean by holding them in a class. It's the result of a selection query from DB and I am going to remove duplicates and store in another table in DB — GeoBeez
– GeoBeez, Commented Dec 10, 2015 at 12:57
Why are you doing duplication removal in Java? You have an RDBMS engine: use it! — fge
– fge, Commented Dec 10, 2015 at 12:59
1-I am not professional i. 2- the order is important for me and based on which items are similar and based on which order I do different things as well and make a relationship tables for them.3-in case, there is a way, so I do not know how to do it! — GeoBeez
– GeoBeez, Commented Dec 10, 2015 at 13:01
You can remove duplicates on database by using 'distinct', 'group by' or something else — Eldar Budagov
– Eldar Budagov, Commented Dec 10, 2015 at 13:02

Eldar Budagov · Accepted Answer · 2015-12-10 13:38:07Z

1

Not best solution, but you can start with this:

    ArrayList<List<String>> bulkUploadList = new ArrayList<List<String>>();
    ArrayList<List<String>> result = new ArrayList<List<String>>();

    HashSet<String> hashSet = new HashSet<>();

    for(List<String> item : bulkUploadList) {
        String title = item.get(1);
        String tags = item.get(2);
        String uniqueString = (title + "#" + tags).trim().toUpperCase();

        if(!hashSet.contains(uniqueString)) {
            result.add(item);
            hashSet.add(uniqueString);
        } else {
            System.out.println("Filtered element " + uniqueString);
        }
    }

edited Dec 10, 2015 at 13:38

answered Dec 10, 2015 at 13:21

Eldar Budagov

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3 Comments

Eldar Budagov Over a year ago

I added conversion to upper case and trim operation, thanks. We can also trim each of parameters separately

GeoBeez Over a year ago

@EldarBudagov hi again. I have another question. I could removed those rows which have the same titles and tags and kept just one of those. How I can find which id in kept list corresponding which removed one?

Eldar Budagov Over a year ago

Use HashMap instead of HashSet to retain binding between id and data

L. Blanc · Accepted Answer · 2015-12-10 19:41:58Z

0

As suggested in one of the comments, you should create a class for the data, make that class implement equals(), and then use HashSet to remove dups. Like this.

class Foo {
String id;
String title;
String tags;
String description;

public boolean equals(Foo this, Foo other) {
   return this.id.equals(other.id) 
      && this.title.equals(other.title)
      && etc.
}

then you can remove dups with

 Set<Foo> set = new LinkedHashSet<Foo>(list);

as Sets do not allow duplication, and the equals() method is used to check.

You should use a linkedHashSet here because you want to preserve the order (according to a comment you made on elsewhere).

You should also implement a hashcode() method consistent with equals().

edited Dec 10, 2015 at 19:41

answered Dec 10, 2015 at 13:29

L. Blanc

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1 Comment

GeoBeez Over a year ago

thanks for writing that I am going to use it as well to learn how to use it :)

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