Linq: List of lists to a long list

Question

I've got an object of type A which consists of a list of objects of type B:

class A { list<B> Alist;}
class B { string C; string D;}

In my program I have a list of A objects:

list<A> listOfA = computeAList();

and I would like to select all the C strings in that list. The following statement I hoped would give me the result I wanted; it returns a list of lists containing the C's:

var query = from objectA in listOfA
            select objectA.Alist.FindAll(x => x.C.Length > 0).C;

Is there a way to get a single list of all the C's instead?

Answer 1

ybo's answer would have been my first response too. The query expression equivalent of this is:

var query = from a in computeAList()
            from b in a.Alist
            select b.C;

For the sake of completeness, the other answers in this thread are variations on the same theme.

From ybo (the exact same query, expressed as dot notation):

var query = listOfA.SelectMany(a => a.Alist, (a, b) => b.C);

From Ray Hayes (including the Where clause; I've reformatted slightly):

var query = listOfA.SelectMany(a => a.AList, (a, b) => b.C)
                   .Where(c => c.Length > 0);

Answer 2

I too would have had a similar answer, my only modification was to add the where clause to avoid having empty strings (where C is empty):

listOfA.SelectMany( a => a.AList, (a, b) => b.C ).Where( c => c.Length > 0 );

Answer 3

An excellent overview of the SelectMany() extension method which is the key thing that allows you to easily create a flattened "list of lists" can be found here: Use LINQ's SelectMany Method to "Flatten" Collections - Dan's IK Blog