Bdtjtk

Hi I have an arraylist of arraylist in this format:

[[val1, val2],[val3,val4],[val1,val2],[val1,val5]]

and would like to get the unique set of arraylists:

[[val1, val2],[val3,val4],[val1,val5]]

I have tried the following:

Set<String> uniques = new HashSet<>();

    for (ArrayList<String> sublist : mappedEntities) {

        uniques.addAll(sublist);

    }

but this merges all the values of the internal arraylist together

can use Java 8 Collection Stream Distinct,

return in Set datatype :

Set<List<String>> uniques = mappedEntities.stream().distinct().collect(Collectors.toSet());

if you want return in List :

List<List<String>> uniques = mappedEntities.stream().distinct().collect(Collectors.toList());

Why not simply put them in a Set like this?

Set<List<String>> uniques = new HashSet<>(mappedEntities);

Your mistake is that you are flattening the inner lists and putting their items in the set separately.

The issue here is that you need a Set of ArrayList Set<ArrayList<String>>, but you are using a Set of Strings Set<String> instead.

Given the list :

List<List<String>> mappedEntities = Arrays.asList(Arrays.asList("val1", "val2"), 

                                                  Arrays.asList("val3", "val4"),

                                                  Arrays.asList("val1", "val2"), 

                                                  Arrays.asList("val1", "val5"));

All you need to do is just declare the set and use the addAll().

Set<List<String>> mySet = new HashSet<>();

mySet.addAll(mappedEntities);

Since a set can hold only unique values, all duplicates will not be added to the set (No need to explicitly check this). You can now print it out :

mySet.forEach(System.out::println);

Or more simply, initialize the HashSet using the list mappedEntities :

Set<List<String>> mySet = new HashSet<>(mappedEntities);

I am beginner on STACKOVERFLOW but i to try solve your problem

I think you want like this..

import java.util.*; 

public class GFG { 

    public static void main(String args) 

    { 

        int n = 3; 



        // Here aList is an ArrayList of ArrayLists 

        ArrayList<ArrayList<String> > aList = 

                new ArrayList<ArrayList<String> >(n); 



        // Create n lists one by one and append to the 

        // master list (ArrayList of ArrayList) 

        ArrayList<String> a1 = new ArrayList<String>(); 

        a1.add("1"); 

        a1.add("2"); 

        aList.add(a1); 



        ArrayList<String> a2 = new ArrayList<String>(); 

        a2.add("11"); 

        a2.add("22"); 

        aList.add(a2); 



        ArrayList<String> a3 = new ArrayList<String>(); 

        a3.add("1"); 

        a3.add("2"); 

        aList.add(a3); 





        Set<ArrayList<String>> uniques = new HashSet<ArrayList<String>>();

        for (ArrayList<String> sublist : aList) {

            uniques.add(sublist);

        }

        System.out.println("Your Answer"); 

        for (ArrayList<String> x : uniques) 

            System.out.println(x); 

    }





    } 

try this code:

public class B {

    public static void main(String args) throws Exception {

       List<List<String>> list= Arrays.asList(

               Arrays.asList("a","b","c"),

               Arrays.asList("a","b","c"),

               Arrays.asList("a","b","c","d"));



       Set<List<String>> uniques = new HashSet<>();

       for (List<String> sublist : list) {

          if(!uniques.contains(sublist))

          uniques.add(sublist);

       }

       System.out.println(uniques);

    }

}

output:

[[a, b, c], [a, b, c, d]]