How to prevent duplicate items from being added to the matrix

Question

I have a matrix that has a set of elements and duplicates I want to add items to ArrayList with no duplicate elements

 package window1;
 import java.util.ArrayList;
  public class Mine {
   public static void main(String[] args) {
     ArrayList<String> listName = new ArrayList<>();

       String sal[]={"val","sa","de","dal","val","sa","de"};

       for(int i =0;i<sal.length;i++){

          listName.add(sal[i]);
                    }

      for(int j=0;j<listName.size();j++){
         System.out.println(listName.get(j));

                    }

            }

      }

This questions has been answered here https://stackoverflow.com/questions/17967114/how-to-efficiently-remove-duplicates-from-an-array-without-using-set — pcgben, Apr 19 '18 at 05:47
Thank you all of the solutions that were developed were good but using HashSet was more accurate and more effective for me Especially when you use it to filter it on BaseAdapter in Android Studio — salem715, Apr 20 '18 at 02:20

Héctor M. · Answer 1 · 2018-04-19T05:59:32.123

You can simply verify if the item exists in your list before adding it, using the contains() method.

The java.util.ArrayList.contains(Object) method returns true if this list contains the specified element.

package window1;

import java.util.ArrayList;

public class Mine {
private ArrayList<String> listName = new ArrayList<>();
private String sal[]={"val","sa","de","dal","val","sa","de"};

     public static void main(String[] args) {

        for(int i =0;i<sal.length;i++)
        {

             if(!listname.contains(sal[i])) // If the element does not exist...
                 listName.add(sal[i]); // Add him
        }

       for(int j=0;j<listName.size();j++) System.out.println(listName.get(j));
    }
}

score 0 · Answer 2 · answered Apr 19 '18 at 05:48

0

You can use contains method :

if(!listName.contains(sal[i]))
                listName.add(sal[i]);

OUTPUT

val
sa
de
dal

(!listName.contains(sal[i]))

contains will return if item already in list and using ! negating the condition.

answered Apr 19 '18 at 05:48

Roushan

4,074
3
21
38

score 0 · Answer 3 · edited Apr 19 '18 at 15:42

0

Set<String> set = new HashSet<String>(listName);

System.out.println("Set values .....");
for (String temp : set) System.out.println(temp);

edited Apr 19 '18 at 15:42

António Ribeiro

4,129
5
32
49

answered Apr 19 '18 at 05:52

sudhan M

1

score 0 · Answer 4 · edited Apr 19 '18 at 08:14

0

Use Hashset to remove duplicates

Set<String> noDupSet = new HashSet<>(Arrays.asList(new String[] {"val1","val2","val1"}));

edited Apr 19 '18 at 08:14

Marco A.

43,032
26
132
246

answered Apr 19 '18 at 05:56

Vasanth Senthamarai Kannan

76
4

score 0 · Answer 5 · answered Apr 19 '18 at 06:20

Either you can use HashSet instead of ArrayList. Example:

HashSet<String> set=new HashSet<String>();  
  set.add("Ravi");  
  set.add("Vijay");  
  set.add("Ravi");  
  set.add("Ajay");  
  //Traversing elements  
  Iterator<String> itr=set.iterator();  
  while(itr.hasNext()){  
   System.out.println(itr.next());  
  }

It will display Ravi, Vijay and Ajay as output. Note Ravi added twice but it adds only once because HashSet contains unique elements only.

Or

If you want to add unique elements in ArrayList then you will need to add items in HashSet first then you can add its item in ArrayList as shown below:

import java.util.ArrayList;
import java.util.HashSet;

public class Main {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ArrayList<String> listName = new ArrayList<String>();
        HashSet<String> newListName = new HashSet<String>();

        String sal[]={"val","sa","de","dal","val","sa","de"};

        // add unique items in HashSet(newListName)
        for(int i=0; i<sal.length; i++){
            newListName.add(sal[i]);
        }

        // add items of HashSet into ArrayList(listName)
        for(String s: newListName) {
            listName.add(s);
        }

        // display ArrayList(listName)
        for(String s: listName) {
            System.out.println(s);
        }
    }
}

score 0 · Answer 6 · answered Apr 19 '18 at 09:48

First convert your array to hashSet.Which will remove the duplicates.

Next convert the HashSet to ArrayList.(Your desired Data Structure collection)

Check The Code bellow.

public static void main(String[] args)
{
        String sal[]={"val","sa","de","dal","val","sa","de"};
        HashSet<String> ss = new HashSet(Arrays.asList(sal));
        System.out.println("HashSet-");
        System.out.println(ss);
        ArrayList<String> asl= new ArrayList<String>(ss);
        System.out.println("ArrayList-");
        System.out.println(asl);
}

O/P:

HashSet-
[de, val, sa, dal]
ArrayList-
[de, val, sa, dal]

How to prevent duplicate items from being added to the matrix

6 Answers6