collections - Give me a practical use-case of Multi-set

Question

I would like to know a few practical use-cases (if they are not related/tied to any programming language it will be better).I can associate Sets, Lists and Maps to practical use cases.

For example if you wanted a glossary of a book where terms that you want are listed alphabetically and a location/page number is the value, you would use the collection TreeMap(OrderedMap which is a Map)

Somehow, I can't associate MultiSets with any "practical" usecase. Does someone know of any uses?

http://en.wikipedia.org/wiki/Multiset does not tell me enough :)

PS: If you guys think this should be community-wiki'ed it is okay. The only reason I did not do it was "There is a clear objective way to answer this question".

Answer 1

Lots of applications. For example, imagine a shopping cart. That can contain more than one instance of an item - i.e. 2 cpu's, 3 graphics boards, etc. So it is a Multi-set. One simple implementation is to also keep track of the number of items of each - i.e. keep around the info 2 cpu's, 3 graphics boards, etc.

I'm sure you can think of lots of other applications.