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
– RubyDigger19, Commented Jul 24, 2018 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
– VeeArr, Commented Jul 24, 2018 at 17:46
Possible duplicate of Remove duplicates from a list of objects based on property in Java 8 — Krzysztof Zieliński
– Krzysztof Zieliński, Commented Jul 24, 2018 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
– Crammeur, Commented Jul 24, 2018 at 17:48

NiVeR · Accepted Answer · 2018-07-24 18:22:47Z

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, 2018 at 18:22

answered Jul 24, 2018 at 17:52

NiVeR

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8 Comments

RubyDigger19 Over a year ago

Obviously, there is something wrong with my equals method because I'm getting back the list with all items in it

NiVeR Over a year ago

@RubyDigger19 You were not giving an Income object to the contains method. Did you change that?

RubyDigger19 Over a year ago

How should I do that?

NiVeR Over a year ago

Look at the code I posted. There is incomesList.get(i) as argument. You are doing some kind of append.

RubyDigger19 Over a year ago

I have this incomesList.get(i) but I don't get it

|

Bharat Satija · Accepted Answer · 2018-07-24 17:59:35Z

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, 2018 at 17:59

Bharat Satija

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3 Comments

Bharat Satija Over a year ago

@RubyDigger19 you are passing incomesList.get(i).month + incomesList.get(i).year in contains method you have to pass Income object -> incomesList.get(i) .

RubyDigger19 Over a year ago

I've create code like this but still getting the same array as original one

Bharat Satija Over a year ago

@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.

Dan · Accepted Answer · 2018-07-24 17:40:47Z

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, 2018 at 17:40

Dan

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4 Comments

RubyDigger19 Over a year ago

I've edited the question with my hashCode and equals. Is it oke if you could check?

Dan Over a year ago

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

RubyDigger19 Over a year ago

Did like you said but still getting the same array with duplicates

Dan Over a year ago

So then something is up with your equals and/or hashCode. Step through the values in the debugger

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