C# Check if any int in list matches any int in another list [duplicate]

Question

I apologize if this is an obvious question, but I cannot find the answer.

Say I have the following:

var list1 = new List<int>{1,2,3};
var list2 = new List<int>{3,5,6};

How can I see if ANY element of list1 is contained in list2? So in this case I want to return true because 3 is in both.

Performing nested loops will not work for me, so it would be ideal if there was a:

list1.HasElementIn(list2);

Answer 1

Use Enumerable.Intersect - it produces intersection of both sequences. If intersection is not empty, then there some item which exists in both sequences:

bool isAnyItemInBothLists = list1.Intersect(list2).Any();

One thing to note - thus Intersect is a deferred streaming operator, then you will get result as soon as any common item will be found. So, you don't need to wait until complete intersection will be computed.