Fastest way to find common items across multiple lists in C#

Question

Given the following:

List> optionLists;

what would be a quick way to determine the subset of Option objects that a

Answer 1

Building on Matt's answer, since we are only interested in options that all lists have in common, we can simply check for any options in the first list that the others share:

var sharedOptions =
    from option in optionLists.First( ).Distinct( )
    where optionLists.Skip( 1 ).All( l => l.Contains( option ) )
    select option;

If an option list cannot contain duplicate entires, the Distinct call is unnecessary. If the lists vary greatly in size, it would be better to iterate over the options in the shortest list, rather than whatever list happens to be First. Sorted or hashed collections could be used to improve the lookup time of the Contains call, though it should not make much difference for a moderate number of items.