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

You could define your own extension method. This version is more verbose, but still readable, and it only enumerates the IEnumerable once:

bool AnyButNotAll(this IEnumerable sequence, Func predicate)
{
    bool seenTrue = false;
    bool seenFalse = false;

    foreach (ItemT item in sequence)
    {
        bool predResult = predicate(item);
        if (predResult)
            seenTrue = true;
        if (!predResult)
            seenFalse = true;

        if (seenTrue && seenFalse)
            return true;
    }

    return false;
}

Much shorter, but enumerates the IEnumerable twice:

bool AnyButNotAll(this IEnumerable sequence, Func predicate)
{
    return sequence.Any(predicate) && !sequence.All(predicate);
}