Question

Given the following:

List<List<Option>> optionLists; 

what would be a quick way to determine the subset of Option objects that appear in all N lists? Equality is determined through some string property such as option1.Value == option2.Value.

So we should end up with List<Option> where each item appears only once.

Answer 1

Ok, this will find the list of Option objects that have a Value appearing in every list.

var x = from list in optionLists         from option in list         where optionLists.All(l => l.Any(o => o.Value == option.Value))         orderby option.Value         select option; 

It doesn’t do a ‘distinct’ select so it’ll return multiple Option objects, some of them with the same Value.