adding the items integer values in java

Question

I have data on following pattern and I just want to add the number of similar items and stored in a List. Whereas , the items like quantity= 1, ingredient=chicken, unit =kg , The unit will be always kg. I have List<itemsDTO> I want to add similar items from this list. [{1,"kg","chicken"} , {2.2,"kg","beaf"} , {0.25,"kg","chicken"}]

public class itemsDTO {

    double quantity;
    String unit;
    String ingredient;

}

I have tried this code

        List<itemsDTO> itemsDTOList = new ArrayList<>();
            for (int i = 0; i < itemsDTOList.size(); i++) {
            for (int j = 0; j < itemsDTOList.size(); j++) {

                if (itemsDTOList.get(i).getIngredient().equalsIgnoreCase(itemsDTOList.get(j).getIngredient())) {
                    int sum;
                    sum = itemsDTOList.get(i).getQuantity() + itemsDTOList.get(j).getQuantity();
                }
            }

        }

Expected Output 1.25 kg chicken,2.2 kg beaf

Hadi · Accepted Answer · 2020-04-22 16:08:19Z

3

You can use toMap collector with merge function:

BinaryOperator<itemsDTO> sumQuantity = (a, b) -> {
        a.setQuantity(a.getQuantity() + b.getQuantity());
        return a;
    };
itemsDTOList.stream()
    .collect(Collectors.toMap(itemsDTO::getIngredient, Function.identity(), sumQuantity))
    .values();

edited Apr 22, 2020 at 16:08

answered Apr 22, 2020 at 15:44

Hadi

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12 Comments

Lily Over a year ago

What is the list in your answer? @Hadi J

Hadi Over a year ago

I meant itemsDTOList

Lily Over a year ago

It is possible that I have chicken is more than 2 times. So, does it work for that condition too?

Hadi Over a year ago

Yes, it is possible. toMap collectors with merge function merge all object with same ingredient

Shoshi Over a year ago

@Lily, i think this solution is absolutely perfect. you should also try by yourself something.

itemsDTOS.stream().collect(Collectors.toMap(ItemsDTO::getIngredient, Function.identity(), sumQuantity))                 .values()                 .stream()                 .map(itemsDTO -> itemsDTO.getQuantity() + " " + itemsDTO.getUnit() + " " + itemsDTO.getIngredient())                 .collect(Collectors.toList());

But above comment is perfect. you would call itemDTO.toString and override toString in your itemDTO class, which will return quantity + " " + unit + " " + ingredient;

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