[Rd] nlevels(<no factor>) is 0 and not NA

[Torsten Hothorn]

> nlevels(c("a", "b"))
[1] 0

but the documentation in R 2.5.0 (and earlier) says

 	If the argument is not a 'factor', 'NA' is returned.

I hope it isn't too late, I only came across this in a lecture this 
morning.

Best,

Torsten