How to get duplicate elements in array list using guava predicates

Question

I have a array with set of elements. I need to find the duplicate elements in that array by comparing particular field using guava predicated in java.

For example:
I have an arraylist with set of employees details. I need to find details of employees with same name.

score 6 · Accepted Answer · edited Nov 15 '16 at 01:54

6

You can use Guava Multimaps.index method:

ImmutableListMultimap<String, Employee> byName = 
  Multimaps.index(employees, new Function<Employee, String>(){
      @Override
      public String apply(Employee e) {
          return e.getName();
      } 
  });

In Java 8:

Map<Department, List<Employee>> byName = 
    employees.stream()
             .collect(Collectors.groupingBy(Employee::getName))

Regarding your comment, it seems that you want to filter the list to keep only employees with a specific name.

So using Guava:

List<Employee> employees = // ...
Collection<Employee> filtered = 
    Collections2.filter(employees, new Predicate<Employee>() {
        @Override
        public boolean apply(Employee e) {
            return e.getName().equals("John Doe");
        }
    });
// if you want a List:
List<Employee> filteredList = new ArrayList<>(filtered);

Using Java 8:

List<Employee> filteredList = employees.stream()
                                       .filter(e -> e.getName().equals("John Doe"))
                                       .collect(Collectors.toList());

edited Nov 15 '16 at 01:54

Pang

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answered Sep 17 '15 at 14:49

Jean Logeart

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What about advertising Java8 lambda expressions here? – Tamas Hegedus Sep 17 '15 at 15:00
@hege_hegedus You got it – Jean Logeart Sep 17 '15 at 15:02
That's even better! I just thought about `Multimaps.index(employees, e -> e.getName())` :) – Tamas Hegedus Sep 17 '15 at 15:08
The above code is just grouping the list based on name. What i need is a List of names that have more than once in that LIST – Krieger Sep 22 '15 at 10:21
@Krieger Can you provide a specific example? – Jean Logeart Sep 22 '15 at 13:07
@ Jean Logeart For example, there is a List of employee details objects . I need to filter employee details from that list by empoyees with same name – Krieger Sep 23 '15 at 12:59
You mean with a specific name, like filtering the list? What my example does is that it groups all employees with the same name. – Jean Logeart Sep 23 '15 at 13:02
Yes, i need filtered list. not grouped list with same name. Is there any way to do in Guava? – Krieger Sep 23 '15 at 14:31
@ Jean Logeart Thanks for answer. Also i need a list with same name employees, but the problem here is i dont know the name. I just need list of employees with name occurs more than once from exsisting List. – Krieger Sep 24 '15 at 08:05

How to get duplicate elements in array list using guava predicates

1 Answers1