Does .NET have a way to check if List a contains all items in List b?

Question

I have the following method:

namespace ListHelper
{
    public class ListHelper<T>
    {
        public static bool ContainsAllItems(List<T> a, List<T> b)
        {
            return b.TrueForAll(delegate(T t)
            {
                return a.Contains(t);
            });
        }
    }
}

The purpose of which is to determine if a List contains all the elements of another list. It would appear to me that something like this would be built into .NET already, is that the case and am I duplicating functionality?

Edit: My apologies for not stating up front that I'm using this code on Mono version 2.4.2.

Answer 1

If you're using .NET 3.5, it's easy:

public static bool ContainsAllItems(List<T> a, List<T> b)
{
    return !b.Except(a).Any();
}

This checks whether there are any elements in b which aren't in a - and then inverts the result.