LINQ Full Join

FullJoin.cs

        public static IEnumerable<TResult> FullJoin<TOuter, TInner, TKey, TResult>(
            this IEnumerable<TOuter> outer,
            IEnumerable<TInner> inner,
            Func<TOuter, TKey> outerKeySelector,
            Func<TInner, TKey> innerKeySelector,
            Func<TOuter, TInner, TResult> resultSelector)
        {
            return from key in outer.Select(outerKeySelector).Union(inner.Select(innerKeySelector))
                   join outerItem in outer on key equals outerKeySelector(outerItem) into outerGroup
                   from outerItem in outerGroup.DefaultIfEmpty()
                   join innerItem in inner on key equals innerKeySelector(innerItem) into innerGroup
                   from innerItem in innerGroup.DefaultIfEmpty()
                   where outerItem == null ^ innerItem == null
                   select resultSelector(outerItem, innerItem);
        }