Arraylist of objects - how to add objects with duplicate values

Question

I have an ArrayList of Dog that looks like this,

ArrayList<Dog> array=new ArrayList<>();

   array.add(new Dog("one", 10));
   array.add(new Dog("two", 20));
   array.add(new Dog("one", 40));

Class Dog takes a String and a Double as parameters.I'm trying to merge those ArrayList objects that have duplicate String values.At the same time i need to add their Double values. So in this example i want to get a new ArrayList that will have two Dog objects like this,

Dog ("one", 50)
Dog ("two", 20)

I've already managed to add objects with duplicate values but i'm having trouble in adding their double values.Any suggestions?

iterate over the list. A dog with this String already exists? add the integer, else, add the dog — Stultuske
– Stultuske, Commented Apr 8, 2016 at 8:25
I would use a map with Map<String, Dog> where the String is the dogs name. Using a list needs more work to handle the duplicates. — Tom
– Tom, Commented Apr 8, 2016 at 8:26

wero · Accepted Answer · 2016-04-08 08:39:14Z

4

You can combine the dogs using Map.merge and a remapping function:

Map<String,Dog> map = new HashMap<>();
array.stream().forEach(dog -> map.merge(dog.name, dog, (d1, d2) -> {
    return new Dog(d1.name, d1.count + d2.count);
}));

ArrayList<Dog> mergedDogs = new ArrayList<>(map.values());

answered Apr 8, 2016 at 8:39

wero

33.1k3 gold badges63 silver badges87 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Siddharth · Accepted Answer · 2016-04-08 08:41:02Z

You can use a Map to track Dog objects as you encounter them while you go through the List one by one in a for loop.

List<Dog> array=new ArrayList<>();

array.add(new Dog("one", 10));
array.add(new Dog("two", 20));
array.add(new Dog("two", 120));
array.add(new Dog("one", 40));

Map<String, Dog> map = new HashMap<>(); //Map with key=StringField and value=Dog object

for(Dog d : array){

    Dog dog = map.get(d.getStringField()); 
    if(dog != null){ //If dog object is already in map
        dog.setDoubleField(dog.getDoubleField()+d.getDoubleField()); //add the double value of d to it.
    }else{
        map.put(d.getStringField(), d); //add the dog object with key as stringField
    }
}

System.out.println(Arrays.asList(map.values().toArray()));

Collectives™ on Stack Overflow

Arraylist of objects - how to add objects with duplicate values

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related