Question

I have a large list (~ 110,000 strings), which I need to compare to a similar sized list.

List A comes from 1 system.
List B comes from a SQL table (I can only read, no stored procs, etc)

What is the best way to find what values are in list A, that no longer exists in list B?

Is 100,000 strings a large number to be handled in an array?

thanks

Answer 1

So you have two lists like so:

List<string> listA;
List<string> listB;

Then use Enumerable.Except:

List<string> except = listA.Except(listB).ToList();

Note that if you want to, say, ignore case:

List<string> except = listA.Except(listB, StringComparer.OrdinalIgnoreCase).ToList();

You can replace the last parameter with an IEqualityComparer<string> of your choosing.