[R] Refactor all factors in a data frame

[hadley wickham]

Hi Hilmar,

Try this:

cat <- sapply(df, is.factor)
df[cat] <- lapply(df[cat], factor)

Hadley

On 6/5/07, Hilmar Berger <hilmar.berger at imise.uni-leipzig.de> wrote:
> 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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