Find items from a list which exist in another list

Question

I have a List

PropA  
{  
    int a;  
    int b;  
}

and another List

Answer 1

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

List first;
List 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.