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Google Collections Distinct Predicate

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

Solution

  • 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