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how to make list of duplicates in custom arraylist Java


By : Faizan Rizvi
Date : September 16 2020, 08:00 AM
may help you . If your Dog instances are in a List your best bet for sorting is using Java's Comparator class with List#sort. You can use the default methods of Comparator to create a comparator on multiple criteria. For example, the following code will sort dogs by tail length, then by name for those that have the same tail length:
code :
List<Dog> dogs = // ...
dogs.sort(
    Comparator.comparing(Dog::getTailLength)
              .thenComparing(Dog::getName));


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java beginner: which is preferred when class has arraylist of arraylist (clone(), unmodifiable list,custom deepcopying)


By : Joe
Date : March 29 2020, 07:55 AM
I hope this helps . If what you try to do is to copy the matrix, bear in mind Double is unmodifiable so, it doesn't make much sense, creating new instances. You can freely copy the references using something like:
List> copy = new ArrayList>(); copy.addAll( original );
code :
copy.get( 0 ) .get( 0 ) = -1.0; 

// original at ( 0,0 ) remains the same ... 
import java.util.Arrays;
import java.util.List;
import java.util.ArrayList;

public class CopyMatrix { 
    public static void main( String [] args ) { 

        Matrix m = new Matrix();
        m.add( Arrays.asList(0.0, 1.0, 2.0 ));
        m.add( Arrays.asList(3.0, 4.0, 5.0 ));
        m.add( Arrays.asList(6.0, 7.0, 8.0 ));

        System.out.println("m = \n" +  m );

        Matrix m1 = m.copy() ;

        m1.get( 0 ).set( 0 , 100.0 );
        m1.get( 2 ).set( 2 , -400.0 );


        System.out.printf( "After m = %n %s %n m1 = %n %s %n", m, m1);
    }
}
class Matrix extends ArrayList<List<Double>> {
    public Matrix copy() {
        Matrix copy = new Matrix();
        for( List<Double> each : this ) { 
            copy.add( new ArrayList<Double>( each ) );
        }
        return copy;
    }
}
 java CopyMatrix 
m = 
[[0.0, 1.0, 2.0], [3.0, 4.0, 5.0], [6.0, 7.0, 8.0]]
After m = 
 [[0.0, 1.0, 2.0], [3.0, 4.0, 5.0], [6.0, 7.0, 8.0]] 
 m1 = 
 [[100.0, 1.0, 2.0], [3.0, 4.0, 5.0], [6.0, 7.0, -400.0]] 

Find duplicates in an ArrayList and set the duplicates to new ArrayList dynamically using Java


By : Judy
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , The best way is to use a Map. Check is the map contains a key of the String. If it doesn't create a new List and add it to the map. If it does, then just add the String the list already in the map.
code :
public static Map<String, List<String>> getMap(List<String> list) {
    Map<String, List<String>> map = new HashMap<>();

    for (String s: list) {
        if (!map.containsKey(s)) {
            List<String> mapList = new ArrayList<>();
            mapList.add(s);
            map.put(s, mapList);
        } else {
            ((List<String>)map.get(s)).add(s);
        }
    } 
    return map;
}
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class TestLIst {

    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        list.add("A");
        list.add("B");
        list.add("A");
        list.add("B");
        list.add("C");
        list.add("D");

        Map<String, List<String>> map = getMap(list);
        printMapAsLists(map);
    }

    public static Map<String, List<String>> getMap(List<String> list) {
        Map<String, List<String>> map = new HashMap<>();

        for (String s: list) {
            if (!map.containsKey(s)) {
                List<String> mapList = new ArrayList<>();
                mapList.add(s);
                map.put(s, mapList);
            } else {
                ((List<String>)map.get(s)).add(s);
            }
        } 
        return map;
    }

    public static void printMapAsLists(Map<String, List<String>> map) {
        for (List<String> list : map.values()) {
            System.out.println(list);
        }
    }
}
[D]
[A, A]
[B, B]
[C]

Remove duplicates from a list in an Arraylist in java


By : Benoit DESTREMAU
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , I checked many examples but i could not applied for my variables. I have a ArratyList Of lists of Strings. , Not best solution, but you can start with this:
code :
    ArrayList<List<String>> bulkUploadList = new ArrayList<List<String>>();
    ArrayList<List<String>> result = new ArrayList<List<String>>();

    HashSet<String> hashSet = new HashSet<>();

    for(List<String> item : bulkUploadList) {
        String title = item.get(1);
        String tags = item.get(2);
        String uniqueString = (title + "#" + tags).trim().toUpperCase();

        if(!hashSet.contains(uniqueString)) {
            result.add(item);
            hashSet.add(uniqueString);
        } else {
            System.out.println("Filtered element " + uniqueString);
        }
    }

How make a List of ArrayList in Java?


By : user2163168
Date : March 29 2020, 07:55 AM
this one helps. The reason for being the last list empty is that Java stores everything in the form of references i.e in the form of memory address and manipulates them in the same way.
Hence ,the ArrayList object list is also a reference. So
code :
ArrayList<ArrayList<Integer>> list_of_lists = new ArrayList<ArrayList<Integer>>();
List<Integer> list = new ArrayList<Integer>();          
for(int x = 0; x < 5; x++) {
    for(int y = 0; y < 2; y++) {                
        list.add(x);
        list.add(y);                
        list_of_lists.add((ArrayList<Integer>) list);
        System.out.println(list_of_lists);
        list.clear();
    }
    System.out.println(list_of_lists); //composes of empty lists 
                                        //the same of times list is added to it
}
System.out.println(list_of_lists);
  ArrayList<ArrayList<Integer>> list_of_lists = new 
    ArrayList<ArrayList<Integer>>();
        List<Integer> list;        
        for(int x = 0; x < 5; x++) {
            for(int y = 0; y < 2; y++) {  
                list = new ArrayList<>();              
                list.add(x);
                list.add(y);                
                list_of_lists.add((ArrayList<Integer>) list);
                System.out.println(list_of_lists);
                // list.clear();
            }
         }
          System.out.println(list_of_lists);
        }

Java ArrayList remove duplicates on a custom condition


By : Lastig
Date : March 29 2020, 07:55 AM
like below fixes the issue I have an array list of items of class , What is the problem with :
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