Create an Array of Unique Values from Similar Objects

Question

I am trying to create an array of unique values based on the properties of a number of identical Objects. These properties will have identical values, but some of them will be null, like so:

Object obj1 = new Object("Value 1", "Value 2", null);
Object obj2 = new Object("Value 1", null, "Value 3");
Object obj3 = new Object(null, "Value2", "Value3")

Object Class

public class Object {
   private String value1;
   private String value2;
   private String value3;

   // Constructor
   public Object(String value1, String value2, String value3){ // this.value1... }

   // Getters & Setters
}

(These Objects can have n number of properties, but assume just 3 for this question)

How can I take the above 3 objects (or any number objects) and quickly combine (or sample) each of their properties to create the below array?

["Value 1", "Value 2", "Value 3"]

I'm thinking a Set could be useful here, but I'm not quite sure how to approach it

I need to know how you have stored those values in your object class. Is your object class constructor is a varargs constructor and you are assigning all the passed values to any array? How can get the passed values from your object? — Amit Bera
– Amit Bera, Commented Mar 14, 2018 at 19:16

Youcef LAIDANI · Accepted Answer · 2018-03-14 19:21:02Z

1

I assume your Object look like this :

class MyObject {

    private String[] inputs;

    public MyObject(String... inputs) {
        this.inputs = inputs;
    }
    //Getters Setter

}

If you are using Java 8 you can use :

MyObject obj1 = new MyObject("Value 1", "Value 2", null);
MyObject obj2 = new MyObject("Value 1", null, "Value 3");
MyObject obj3 = new MyObject(null, "Value 2", "Value 3");

Set<String> result = Arrays.asList(obj1, obj2, obj3)
        .stream()
        .flatMap(item -> Stream.of(item.getInputs()))
        .filter(item -> item != null)
        .collect(Collectors.toSet());

System.out.println(result);

Outputs

[Value 3, Value 1, Value 2]

answered Mar 14, 2018 at 19:21

Youcef LAIDANI

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Comments

Amit Bera · Accepted Answer · 2018-03-14 19:33:41Z

1

Try the below solution :

public class Main {
    public static void main(String[] args) throws InterruptedException, ExecutionException {
        MyObject obj1 = new MyObject("Value 1", "Value 2", null);
        MyObject obj2 = new MyObject("Value 1", null, "Value 3");
        MyObject obj3 = new MyObject(null, "Value 2", "Value 3");

        System.out.println(myObjectPropToStringArray(obj1,obj2,obj3));


    }

    public static Set<String> myObjectPropToStringArray(MyObject... myObject) {
        Set<String> result = new HashSet<>();
        Arrays.stream(myObject).forEach(e ->{

            result.add(e.getValue1());
            result.add(e.getValue2());
            result.add(e.getValue3());
        });
        return result;
    }
}

 class MyObject {
       private String value1;
       private String value2;
       private String value3;



    public MyObject(String value1, String value2, String value3) {
        super();
        this.value1 = value1;
        this.value2 = value2;
        this.value3 = value3;
    }

    public String getValue1() {
        return value1;
    }

    public void setValue1(String value1) {
        this.value1 = value1;
    }

    public String getValue2() {
        return value2;
    }

    public void setValue2(String value2) {
        this.value2 = value2;
    }

    public String getValue3() {
        return value3;
    }

    public void setValue3(String value3) {
        this.value3 = value3;
    }
 }

answered Mar 14, 2018 at 19:33

Amit Bera

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1 Comment

GuiSim Over a year ago

I would advise against using side effects to add to the result set and instead use flatMap with Streams.of(e.getValue1(), e.getValue2(), e.getValue3()) followed by collect(Collectors.toSet())

ernest_k · Accepted Answer · 2018-03-14 19:30:46Z

If your intention is just to pick all distinct values in each field of those objects, then you can work with lists of each field's values:

List<Object> objects = Arrays.asList(new Object("Value 1", "Value 2", null), 
          new Object("Value 1", null, "Value 3"), 
          new Object(null, "Value2", "Value3");

//This should give you the first list...
List<String> values = objects.stream().map(o ->
             Arrays.asList(o.getVal1(), o.getVal2(), o.getVal3()))
             .distinct()
             .findFirst().get();

//If you need to prefer non-null values, then you can use
//an ordered stream:
List<String> values = objects.stream()
            .map(o ->
                 Arrays.asList(o.getVal1(), o.getVal2(), o.getVal3()))
            .distinct().ordered(list -> 
                (list.get(0) != null ? -1 : 1)
              + (list.get(1) != null ? -1 : 1)
              + (list.get(2) != null ? -1 : 1))
            .findFirst()
            .get();

The comparator implementation is just to make non-null values come at the beginning of the stream so that findFirst can hit them first. Of course you will need to check if the optional has a value.

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