R devel - Mar 2007 - (PR#9578) rbind.data.frame reacts on levels without factor

Brian wrote:
> In your data frames, 'y' is a category
...
> The behaviour is compatible with S apart from the comment in=20
> the R help=20
> page.  That categories are promoted to factors is consistent=20
> with the help for 'category'.
I have been around S and R for about 10 years, but had
never heard of categories before.
All information I get about categories via=20
  ?category=20
in R 2.4.1 is
  'category' has been an old-S function before there were factors;
  should be replaced by 'factor' throughout!

Maybe it's time to drop this particular backwards compatibility=20
feature from rbind?

  Lutz
> It is not a bug, but the help page could say what happens for=20
> categories.
>=20
> On Fri, 23 Mar 2007, Lutz Prechelt wrote:
>=20
> > I am sorry.
> > Here is a minimal example:
> >
> > a=3Ddata.frame(x=3Dc(1:3),y=3Dunclass(factor(c(5:7))))
> > b=3Ddata.frame(x=3Dc(11:13),y=3Dunclass(factor(c(7:9))))
> > rbind(a,b)