Question

This should be simple but I could not wrap my head around it.. Here is how I am doing it now but it seems so wasteful.

There is a

List<string> committees

and

List<string> P.committees

I just want to see if one list has any strings that are contained in the other.

  List<Person> listFilteredCommitteesPerson = new List<Person>();

            foreach (Person p in listFilteredPerson)
            {
                foreach (string strCommittee in p.Committees)
                {
                       if (committees.Contains(strCommittee))
                       {
                           listFilteredCommitteesPerson.Add(p);
                       }
                }
            }

            listFilteredPerson = listFilteredCommitteesPerson;

Answer 1

For a boolean value:

var match = 
   committees.Intersect(listFilteredPerson.SelectMany(p => p.Committees)).Any();

If you want a collection of Person that have a match you can use:

var peopleThatMatch = 
    listFilteredPerson.Where(p => committees.Intersect(p.Committees).Any());

or:

var peopleThatMatch = 
    listFilteredPerson.Where(p => p.Committees.Any(s => committees.Contains(s)));

You might want to consider another collection type (e.g. HashSet<T>) for performance reasons if you have large collections.