Question

I have two lists and I need to compare them and only return a List of Items not in both.

var listOfIds = new List<int> {1,2,4};

var persons = new ObservableCollection<Person>
{
    new Person {Id = 1, Name = "Person 1"},
    new Person {Id = 2, Name = "Person 2"},
    new Person {Id = 3, Name = "Person 3"},
    new Person {Id = 4, Name = "Person 4"}
};

In this example new Person {Id = 3, Name = "Person 3"} would be the result.
A Linq solution would be preferred.

Answer 1

not in will work for you

var listOfIds = new List<int> {1,2,4};

var query = from item in persons 
            where !listOfIds .Contains( item.id )
            select item;

You can check for more detail : SQL to LINQ ( Case 7 – Filter data by using IN and NOT IN clause)