Question

Let’s assume I have 2 List<T> List1 and List2 that look like this:

List 1:

[ID:1, Name:"item1"]
[ID:2, Name:"item2"]
[ID:3, Name:"item3"]
[ID:4, Name:"item4"]

List 2:

[ID:2, Name:"item2"]
[ID:3, Name:"item3"]
[ID:5, Name:"item5"]
[ID:6, Name:"item6"]

How can I get a list that contains only the objects that are in both lists? Using the example above, I want to return:

[ID:2, Name:"item2"]
[ID:3, Name:"item3"]

Modifying the original lists is OK. What’s the best way to do this?

Answer 1

  var result = list1.Intersect(list2).ToList();

Is the most succinct. However keep in mind it is using the default equality comparer which may or may not work for you. If not, you can provide your own:

    public class MyEqualityComparer : IEqualityComparer<Foo>
    {
        public bool Equals(Foo x, Foo y)
        {
            return x.Id == y.Id;
        }

        public int GetHashCode(Foo obj)
        {
            return obj.Id.GetHashCode();
        }
    }

  var result = list1.Intersect(list2, new MyEqualityComparer()).ToList();