[R] Refactor all factors in a data frame

[John Fox]

Dear Hilmar,

You could use something like

DF <- as.data.frame(lapply(DF, function (x) if (is.factor(x)) factor(x) else
x))

Where DF is the data frame.

I hope this helps,
 John

--------------------------------
John Fox, Professor
Department of Sociology
McMaster University
Hamilton, Ontario
Canada L8S 4M4
905-525-9140x23604
http://socserv.mcmaster.ca/jfox 
-------------------------------- 

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Hilmar Berger
> Sent: Tuesday, June 05, 2007 8:20 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Refactor all factors in a data frame
> 
> 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
> 
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