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 class ListHelper<T> {     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.

Note that it would be slightly more conventional to make the method generic rather than the class, and there's no reason to require List<T> instead of IEnumerable<T> - so this would probably be preferred:

public static class LinqExtras // Or whatever {     public static bool ContainsAllItems<T>(this IEnumerable<T> a, IEnumerable<T> b)     {         return !b.Except(a).Any();     } } 

Answer 2

Included in .NET 4: Enumerable.All

public static bool ContainsAll<T>(IEnumerable<T> source, IEnumerable<T> values) {     return values.All(value => source.Contains(value)); }