Google Collections Distinct Predicate

Question

How would one implement a distinct predicate for use with the Google Collections Collections2.filter method?

Answer 1

If I understand you correctly, I'm not sure that Predicate is the right solution here:

Creating a predicate like that would require maintaining some sort of state (ie: maintaining a Set of things it has seen already). This is explicitly advised against in the javadoc.

The usual way to get the distinct items in a collection would be to just add them all to a set. ie:

Set<T> uniqueItems = Sets.newHashSet(collectionWithPotentialDuplicates);

If the equals() and hashCode() methods on <T> don't define uniqueness the way you want, then you should write a utility method that operates on a Collection<T> and a Function<T, Object> which returns the items of type T which are unique after being converted using the Function