Find items from a list which exist in another list

Question

I have a List<PropA>

PropA   {       int a;       int b;   } 

and another List<PropX>

PropX   {       int a;       int b;   } 

Now i have to find items from List<PropX> which exist in List<PropA> matching b property using lambda or LINQ.

Answer 1

ListA.Where(a => ListX.Any(x => x.b == a.b)) 

Answer 2

What you want to do is Join the two sequences. LINQ has a Join operator that does exactly that:

List<PropX> first; List<PropA> second;  var query = from firstItem in first     join secondItem in second     on firstItem.b equals secondItem.b     select firstItem; 

Note that the Join operator in LINQ is also written to perform this operation quite a bit more efficiently than the naive implementations that would do a linear search through the second collection for each item.