Remove duplicates based on property and predicate in Java 8

Question

Question based on https://stackoverflow.com/a/29671501/2517622

Given a list of employees with id, name and IQ:

List<Employee> employee = Arrays.asList(new Employee(1, "John", 80), new Employee(1, "Bob", 120), Employee(1, "Roy", 60), new Employee(2, "Alice", 100));

I want to output:

[Employee{id=1, name='Bob', iq=120}, Employee{id=2, name='Alice', iq=100}]

So, remove duplicates from the list based on id property of employee and choose employee with the highest IQ for obvious reasons. :)

Particularly, I am interested in adjusting this solution which removes duplicates only based on id:

    import static java.util.Comparator.comparingInt;
    import static java.util.stream.Collectors.collectingAndThen;
    import static java.util.stream.Collectors.toCollection;

    ...
    List<Employee> unique = employee.stream()
                                    .collect(collectingAndThen(toCollection(() -> new TreeSet<>(comparingInt(Employee::getId))),
                                                               ArrayList::new));

Is there a way?

List<Employee> unique = employee.stream() .collect(collectingAndThen(toMap(Employee::getId, Function.identity(), BinaryOperator.maxBy(Comparator.comparingInt(Employee::getIq))), m -> new ArrayList<>(m.values()))); — Holger
– Holger, Commented Mar 28, 2019 at 15:28

Ravindra Ranwala · Accepted Answer · 2019-03-28 15:32:17Z

7

How about this,

Collection<Employee> distinctEmps = employee.stream()
    .collect(Collectors.toMap(Employee::getId, Function.identity(), 
        (e1, e2) -> e1.getIq() >= e2.getIq() ? e1 : e2))
    .values();

Another variant by merely following @Holgers approach would be,

Collection<Employee> distinctEmps = employee.stream()
    .collect(Collectors.toMap(Employee::getId, Function.identity(), 
        BinaryOperator.maxBy(Comparator.comparing(Employee::getIq))))
    .values();

edited Mar 28, 2019 at 15:32

answered Mar 28, 2019 at 15:26

Ravindra Ranwala

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