Is there a better way of calling LINQ Any + NOT All?

Question

I need to check if a sequence has any items satisfying some condition but at the same time NOT all items satisfying the same condition.

For example, for a sequence of 10

Answer 1

That is likely a fairly optimal solution if the source is a database. This extension method might be better depending on your source (I think, I just threw it together -- likely many many errors, consider it more pseudo code). The benefit here is it only enumerates once and does a short-circuit as soon as it has read enough to determine the outcome:

static bool SomeButNotAll(this IEnumerable source,
                                   Func predicate)
{
   using(var iter=source.GetEnumerator())
   {
     if (iter.MoveNext())
     {
       bool initialValue=predicate(iter.Current);
       while (iter.MoveNext())
         if (predicate(iter.Current)!=initialValue)
           return true;
     }
   }     
   return false; /* All */
}