According to the reply provided by devReddit here, I did grouping of CSV records (same client names) of following test file (fake data): CSV test file Client Entity Program Final Result (Grouped by Center) What I Need I need to assign a unique value to each group of repeated records, starting over each time center value changes, even keeping the

Assign unique value to field in duplicate records group during groupingBy

According to the reply provided by devReddit here, I did grouping of CSV records (same client names) of following test file (fake data):

CSV test file

id,name,mother,birth,center
1,Antonio Carlos da Silva,Ana da Silva, 2008/03/31,1
2,Carlos Roberto de Souza,Amália Maria de Souza,2004/12/10,1
3,Pedro de Albuquerque,Maria de Albuquerque,2006/04/03,2
4,Danilo da Silva Cardoso,Sônia de Paula Cardoso,2002/08/10,3
5,Ralfo dos Santos Filho,Helena dos Santos,2012/02/21,4
6,Pedro de Albuquerque,Maria de Albuquerque,2006/04/03,2
7,Antonio Carlos da Silva,Ana da Silva, 2008/03/31,1
8,Ralfo dos Santos Filho,Helena dos Santos,2012/02/21,4
9,Rosana Pereira de Campos,Ivana Maria de Campos,2002/07/16,3
10,Paula Cristina de Abreu,Cristina Pereira de Abreu,2014/10/25,2
11,Pedro de Albuquerque,Maria de Albuquerque,2006/04/03,2
12,Ralfo dos Santos Filho,Helena dos Santos,2012/02/21,4

Client Entity

package entities;

public class Client {

    private String id;
    private String name;
    private String mother;
    private String birth;
    private String center;
    
    public Client() {
    }

    public Client(String id, String name, String mother, String birth, String center) {
        this.id = id;
        this.name = name;
        this.mother = mother;
        this.birth = birth;
        this.center = center;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getMother() {
        return mother;
    }

    public void setMother(String mother) {
        this.mother = mother;
    }

    public String getBirth() {
        return birth;
    }

    public void setBirth(String birth) {
        this.birth = birth;
    }

    public String getCenter() {
        return center;
    }

    public void setCenter(String center) {
        this.center = center;
    }
        
    @Override
    public String toString() {
        return "Client [id=" + id + ", name=" + name + ", mother=" + mother + ", birth=" + birth + ", center=" + center
                + "]";
    }
        
}

Program

package application;
    
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
    
import entities.Client;
    
public class Program {
    
    public static void main(String[] args) throws IOException {
            
        Pattern pattern = Pattern.compile(",");
            
        List<Client> file = Files.lines(Paths.get("src/Client.csv"))  
            .skip(1)
            .map(line -> { 
                String[] fields = pattern.split(line);
                return new Client(fields[0], fields[1], fields[2], fields[3], fields[4]);
            })
            .collect(Collectors.toList()); 
                        
        Map<String, List<Client>> grouped = file
            .stream()
            .filter(x -> file.stream().anyMatch(y -> isDuplicate(x, y)))
            .collect(Collectors.toList())
            .stream()
            .collect(Collectors.groupingBy(p -> p.getCenter(), LinkedHashMap::new, Collectors.mapping(Function.identity(), Collectors.toList())));

        grouped.entrySet().forEach(System.out::println);    
    }
}

private static Boolean isDuplicate(Client x, Client y) {

    return !x.getId().equals(y.getId())
    && x.getName().equals(y.getName())
    && x.getMother().equals(y.getMother())
    && x.getBirth().equals(y.getBirth());    
}

Final Result (Grouped by Center)

1=[Client [id=1, name=Antonio Carlos da Silva, mother=Ana da Silva, birth= 2008/03/31, center=1],
    Client [id=7, name=Antonio Carlos da Silva, mother=Ana da Silva, birth= 2008/03/31, center=1]]
2=[Client [id=3, name=Pedro de Albuquerque, mother=Maria de Albuquerque, birth=2006/04/03, center=2],
    Client [id=5, name=Ralfo dos Santos Filho, mother=Helena dos Santos, birth=2012/02/21, center=2],
    Client [id=6, name=Pedro de Albuquerque, mother=Maria de Albuquerque, birth=2006/04/03, center=2],
    Client [id=8, name=Ralfo dos Santos Filho, mother=Helena dos Santos, birth=2012/02/21, center=2],
    Client [id=11, name=Pedro de Albuquerque, mother=Maria de Albuquerque, birth=2006/04/03, center=2],
    Client [id=12, name=Ralfo dos Santos Filho, mother=Helena dos Santos, birth=2012/02/21, center=2]]

What I Need

I need to assign a unique value to each group of repeated records, starting over each time center value changes, even keeping the records together, since map does not guarantee this, according to the example below:

Numbers at left show the grouping by center (1 and 2). Repeated names have the same inner group number and start from “1”. When the center number changes, the inner group numbers should be restarted from “1” again and so on.

    1=[Client [group=1, id=1, name=Antonio Carlos da Silva, mother=Ana da Silva, birth= 2008/03/31, center=1],
       Client [group=1, id=7, name=Antonio Carlos da Silva, mother=Ana da Silva, birth= 2008/03/31, center=1]]

 // CENTER CHANGED (2) - Restart inner group number to "1" again.

    2=[Client [group=1, id=3, name=Pedro de Albuquerque, mother=Maria de Albuquerque, birth=2006/04/03, center=2],
       Client [group=1, id=6, name=Pedro de Albuquerque, mother=Maria de Albuquerque, birth=2006/04/03, center=2],
       Client [group=1, id=11, name=Pedro de Albuquerque, mother=Maria de Albuquerque, birth=2006/04/03, center=2],
 
// NAME CHANGED, BUT SAME CENTER YET - so increases by "1" (group=2)
      
Client [group=2, id=5, name=Ralfo dos Santos Filho, mother=Helena dos Santos, birth=2012/02/21, center=2],
       Client [group=2, id=8, name=Ralfo dos Santos Filho, mother=Helena dos Santos, birth=2012/02/21, center=2],
       Client [group=2, id=12, name=Ralfo dos Santos Filho, mother=Helena dos Santos, birth=2012/02/21, center=2]]

Answer

Instead of using file.stream within each filter, you could create a map by forming a key using the relevant fields:

A new method in Client class

public String getKey() {
    return String.format("%s~%s~%s~%s", id, name, mother, birth);
}

Use this to create a map with the count as value.

Map<String, Long> countMap = 
    file.stream()
        .map(Client::getKey)
        .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

Then

// For each inner group you need a separate id based on the name.
// The input would be a map with client name as the key and the
// value would be the corresponding list of clients.
// The below function returns a new map with 
// integer as the key part (required unique id for each inner group).
Function<Map<String, List<Client>>, Map<Integer, List<Client>>> mapper
    = map -> {
        AtomicInteger i = new AtomicInteger(1);
        return map.entrySet().stream()
                  .collect(Collectors.toMap(e -> i.getAndIncrement(), Map.Entry::getValue);
    };

// assuming static import of "java.util.stream.Collectors"
Map<String, Map<Integer, List<Client>>> grouped = 
    file.stream()
        .filter(x -> countMap.get(x.getKey()) > 1L) // indicates duplicate
        .collect(groupingBy(Client::getCenter,    
                            collectingAndThen(groupingBy(Client::getName, toList()),
                                              mapper /* the above function*/ )));

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Answer