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

var nonmanagers = employees.Select(e => e.Id)
    .Except(managers.Select(m => m.EmployeeId))
    .Select(id => employees.Single(e => e.Id == id));

Answer 2

    /// <summary>
    /// This method returns items in a set that are not in 
    /// another set of a different type
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <typeparam name="TOther"></typeparam>
    /// <typeparam name="TKey"></typeparam>
    /// <param name="items"></param>
    /// <param name="other"></param>
    /// <param name="getItemKey"></param>
    /// <param name="getOtherKey"></param>
    /// <returns></returns>
    public static IEnumerable<T> Except<T, TOther, TKey>(
                                           this IEnumerable<T> items,
                                           IEnumerable<TOther> other,
                                           Func<T, TKey> getItemKey,
                                           Func<TOther, TKey> 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.