Using LINQ to Objects to find items in one collection that do not match another

Question

I want to find all items in one collection that do not match another collection. The collections are not of the same type, though; I want to write a lambda expression to spe

Answer 1

    /// 

    /// This method returns items in a set that are not in 
    /// another set of a different type
    /// 
    /// 
    /// 
    /// 
    /// 
    /// 
    /// 
    /// 
    /// 
    public static IEnumerable Except(
                                           this IEnumerable items,
                                           IEnumerable other,
                                           Func getItemKey,
                                           Func getOtherKey)
    {
        return from item in items
               join otherItem in other on getItemKey(item)
               equals getOtherKey(otherItem) into tempItems
               from temp in tempItems.DefaultIfEmpty()
               where ReferenceEquals(null, temp) || temp.Equals(default(TOther))
               select item;
    }

I don't remember where I found this method.