How to create new array from existing without duplicate elements

Question

I have an array of objects in java. Something like this

array = [{month: 6, year: 2018, amount: 242}, {month: 6, year: 2018, amount: 345}, {month: 7, year: 2018, amount: 4567}, {month: 7, year: 2018, amount: 1234}, {month: 8, year: 2018, amount: 211}]

So I want to create a new array without duplicate month and year keys so this new array should look like this

newArray = [{month: 6, year: 2018}, {month: 7, year: 2018}, {month: 8, year: 2018}]

Here is function that I've implemented

private class IncomeArrayAdapter extends BaseAdapter {
        private LayoutInflater inflater;
        private List<Income> incomeList;
        List<Income> listOfIncomes = new ArrayList<>();

        public IncomeArrayAdapter(List<Income> incomesList) {
            boolean found = false;
            inflater = LayoutInflater.from(getActivity());
            this.incomeList = incomesList;
            for (int i = 0; i < incomeList.size(); i++) {
                if (!listOfIncomes.contains(incomesList.get(i).month + incomesList.get(i).year)) {
                    listOfIncomes.add(incomesList.get(i));
                }
            }
}

So I've tried with hashCode() and equals() functions but I'm new to java and I failed. So I would like if some could help me and explain to me how to create this new array?

EDIT:

   @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        if (!super.equals(o)) return false;
        Income income = (Income) o;
        return month == income.month &&
                year == income.year;
    }

    @Override
    public int hashCode() {

        return Objects.hash(super.hashCode(), month, year);
    }

here is my hashCode() and equals() implementation. It should return only one list object if month and year are equal.

I have 5 objects in incomeList and listOfIncomes returns the same list — RubyDigger19, Jul 24 '18 at 17:43
hint: For `contains` to work the way you want it to, you should be passing an `Income` to it. It looks like you're passing either a `String` or an `int` (depending on what the types of `month` and `year` are). — VeeArr, Jul 24 '18 at 17:46
Possible duplicate of [Remove duplicates from a list of objects based on property in Java 8](https://stackoverflow.com/questions/29670116/remove-duplicates-from-a-list-of-objects-based-on-property-in-java-8) — Krzysztof Zieliński, Jul 24 '18 at 17:47
What i suggest you is too redefine your class `Income` extends new abstract class `AbstractIncome` where you put filed `month` and `years` and you put `amount` in the `Income` class — Crammeur, Jul 24 '18 at 17:48

NiVeR · Accepted Answer · 2018-07-24T18:22:47.567

1

Assuming your equals implementation is correct, you should modify the if-statement in the following way to make use of it:

...
if (!listOfIncomes.contains(incomesList.get(i))) 
{
    listOfIncomes.add(incomesList.get(i));
} 
...

also another suspicious thing that I see is in the equals implementation, in particular the line:

if (!super.equals(o)) return false;

try removing it and try again.

edited Jul 24 '18 at 18:22

answered Jul 24 '18 at 17:52

NiVeR

9,644
4
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Obviously, there is something wrong with my equals method because I'm getting back the list with all items in it – RubyDigger19 Jul 24 '18 at 18:04
@RubyDigger19 You were not giving an `Income` object to the contains method. Did you change that? – NiVeR Jul 24 '18 at 18:05
How should I do that? – RubyDigger19 Jul 24 '18 at 18:07
Look at the code I posted. There is `incomesList.get(i)` as argument. You are doing some kind of append. – NiVeR Jul 24 '18 at 18:08
I have this `incomesList.get(i)` but I don't get it – RubyDigger19 Jul 24 '18 at 18:10
You don't get what? – NiVeR Jul 24 '18 at 18:11
I don't understand. I've set the code you said but my array is still the same like original one – RubyDigger19 Jul 24 '18 at 18:12
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/176669/discussion-between-niver-and-rubydigger19). – NiVeR Jul 24 '18 at 18:15

score 1 · Answer 2 · answered Jul 24 '18 at 17:59

1

You have to update if statement and pass income object in contains method. contains method internally calls equals methods.

 for (int i = 0; i < incomeList.size(); i++) { 
     if (!listOfIncomes.contains(incomesList.get(i)) {
                listOfIncomes.add(incomesList.get(i));
     }
 }

answered Jul 24 '18 at 17:59

Bharat Satija

362
1
13

@RubyDigger19 you are passing `incomesList.get(i).month + incomesList.get(i).year` in `contains` method you have to pass `Income object -> incomesList.get(i)` . – Bharat Satija Jul 24 '18 at 18:09
I've create code like this but still getting the same array as original one – RubyDigger19 Jul 24 '18 at 18:14
1

@RubyDigger19 I just ran the code and removed this if statement `if (!super.equals(o)) return false;` and it worked for me.Can you remove this line `if (!super.equals(o)) return false;` from the code and try. – Bharat Satija Jul 24 '18 at 18:29

score 0 · Answer 3 · answered Jul 24 '18 at 17:40

0

Set<Income> uniqueSets = Sets.newHashSet(incomesList); should do the trick.

Just make sure the equals and hashCode methods are setup the way you're expecting the logic to work.

answered Jul 24 '18 at 17:40

Dan

979
1
8
29

I've edited the question with my `hashCode` and `equals`. Is it oke if you could check? – RubyDigger19 Jul 24 '18 at 17:48
Your `equals` and `hashcode` only seem to care about the month and year. I'd just make sure those values are the same. I'd convert the `List` into a `Set`, which will make all the values unique. If necessary, then convert it back or just return the `Set` – Dan Jul 24 '18 at 17:52
Did like you said but still getting the same array with duplicates – RubyDigger19 Jul 24 '18 at 18:01
So then something is up with your `equals` and/or `hashCode`. Step through the values in the debugger – Dan Jul 24 '18 at 18:04

How to create new array from existing without duplicate elements

3 Answers3