Question

Google Collections contains the Multiset interface and the TreeMultiset class, but I was surprised to find that there is no corresponding SortedMultiset interface.

Something like that would be very useful for modelling discrete probability distributions.

Before I attempt to implement it myself, I would like to know if there is a specific reason for leaving it out, e.g. likely violation of Multiset or Collection invariants, or inherent performance problems etc.

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Edit: I didn’t realise it originally but this is actually 3 separate requests:

1. A change to the return type of one method (TreeMultiset.entrySet)
2. An new interface to match the existing functionality of TreeMultiset
3. A new pair of methods to sum the counts in branches of the tree

Answer 1

I think it’s just that no one’s ever needed it yet, so we haven’t written it yet. It’s something I’d consider.