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?

Jon Skeet · Accepted Answer · 2009-03-16 11:10:33Z

57

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);

edited Mar 16, 2009 at 11:10

answered Mar 16, 2009 at 9:50

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

ybo Over a year ago

@Jon, sorry I didn't see your comment. Now you can include Ray's answer ;). Thanks to both you and Ray.

Stachu Over a year ago

I've been to this answer about 20 times so far. I don't know why I can't remember "selectmany" and always try "selectall", but it always happens. Lucky this is always just one google away!

Ray Hayes · Accepted Answer · 2009-03-16 10:06:31Z

17

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 );

answered Mar 16, 2009 at 10:06

Ray Hayes

15k8 gold badges57 silver badges80 bronze badges

Collectives™ on Stack Overflow

Linq: List of lists to a long list

2 Answers 2

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related