[Rd] c.factor

[Matthew Dowle]

> Just for clarification, my interest was only to provide an 
> alternative that provided for a more generic approach, at 
> least in a narrow application, not that I was advocating it's 
> need.

Understood, apologies for falsely implying your advocation.

> I would agree with Prof. Ripley's comments, that one needs to 
> be quite careful in manipulating factors in this fashion, not 
> the least of which would be ordered factors, which have not 
> been considered here and could/would introduce their own 
> idiosyncrasies in this context.

I agree with that of course.

> If something like this gets implemented (ie. concat()) one 
> would need to fully understand the behavioral subtleties and 
> the nature of the results, lest naive users find themselves 
> in the potential presence of cascading errors.

Agree with that too.