Remove duplicates using Streams | Kuchup interview prep

The 30 second answer

I call distinct and collect to a list. On ordered streams the first occurrence is kept. If uniqueness is by a field like email, I toMap with that key, keep the first value on collision, and use LinkedHashMap to preserve order.

List<T> unique = list.stream().distinct().toList();

Keeps the first occurrence for ordered streams (stable).

By a key (for example unique by email):

Collection<Employee> uniqueByEmail = emps.stream()
    .collect(Collectors.toMap(
        Employee::email,
        Function.identity(),
        (a, b) -> a,
        LinkedHashMap::new))
    .values();

Sources:

Stream.distinct
Collectors.toMap

Sources (0)

See inline citations in the answer above.