Intersect LINQ query

Question

If I have an IEnumerable where ClassA exposes an ID property of type long. Is it possible to use a Linq query to get all instances of ClassA with ID belonging to a second IE

Answer 1

Yes.

As other people have answered, you can use Where, but it will be extremely inefficient for large sets.

If performance is a concern, you can call Join:

var results = original.Join(idsToFind, o => o.Id, id => id, (o, id) => o);

If idsToFind can contain duplicates, you'll need to either call Distinct() on the IDs or on the results or replace Join with GroupJoin (The parameters to GroupJoin would be the same).