How do I group by a Nested property's Nested property (part II)

In a previous post (http://bit.ly/bbIthV) i asked how to Group a list of Persons by their nested Address.State, when Address might be null.

Jon Skeet gave a perfect answer to my question:

//Create a dummy replacement for when a person has no addresses Address dummyAddress = new Address { State = "" }; people开发者_Go百科.GroupBy(p => (p.Addresses.GetFirstOrDefault() ?? dummyAddress).State);

But seeing the results, I see that I wasn't asking the right quesion.

If I have 6 people, each one living at n addresses, the above will only get 6 groups...whereas I should instead be getting a group of persons, grouped by the key State that could be found by:

var distinctAddresses = people.SelectMany(p=>p.Addresses).City).Distint();

I think the answer will involve a GroupJoin of some kind, but I haven't gotten very far...

//Back where I started: var y = addresses.GroupJoin(persons,a => a.State, p => p.Addresses.FirstOrDefault(), (a,p)=> p); //Doesn't compile... var y = addresses.GroupJoin(persons,a => a, p => p.Addresses, (a,p)=> p);

Does anybody have a suggestion on how to proceed?

Thank you very much!

It might be simpler using query syntax:

var q = from p in People
        group p by p.Address.State into g
        select g;

How about this?

var q =
    (from p in people
     from a in p.Addresses
     group p by a.State ?? "")
    .ToDictionary(x => x.Key, x => x.Distinct())