Check List for duplications with optional words to exclude

Question

I have a method as below. Method return either false/true either when list contains duplicates or not. I would like to extend my method to say for instance (optional) that i

Answer 1

You can use Except(). From MSDN:

Produces the set difference of two sequences by using the default equality comparer to compare values.

return list.Except(listToExclude).GroupBy(n => n).Any(c => c.Count() > 1);