[R] Refactor all factors in a data frame

[Hilmar Berger]

Hi all,

Assume I have a data frame with numerical and factor variables that I 
got through merging various other data frames and subsetting the 
resulting data frame afterwards. The number levels of the factors seem 
to be the same as in the original data frames, probably because subset() 
calls [.factor without drop = TRUE (that's what I gather from scanning 
the mailing lists).

I wonder if there is a easy way to refactor all factors in the data 
frame at once. I noted that fix(data_frame) does the trick, however, 
this needs user interaction, which I'd like to avoid. Subsequent 
write.table / read.table would be another option but I'm not sure if R 
can guess the factor/char/numeric-type correctly when reading the table.

So, is there any way in drop the unused factor levels from *all* factors 
of a data frame without import/export ?

Thanks in advance,
Hilmar

-- 

Hilmar Berger
Studienkoordinator
Institut für medizinische Informatik, Statistik und Epidemiologie
Universität Leipzig
Härtelstr. 16-18
D-04107 Leipzig

Tel. +49 341 97 16 101
Fax. +49 341 97 16 109
email: hilmar.berger at imise.uni-leipzig.de