[R] Refactor all factors in a data frame

[hadley wickham]

Hi Hilmar,

What was wrong with my solution?  It's much simpler and shorter.

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,
>
> the best solution I found so far is (assuming <data> is your data.frame):
>
> # identify all factor variables
>
> factor.list = colnames(data)[sapply(data,class) == "factor"]
>
> # use transform to apply factor() to all factor variables
> trans.vars
> =paste(factor.list,"=factor(",factor.list,")",sep="",collapse="," )
> data = eval(parse(text=paste("transform(data,",trans.vars,")")))
>
> Regards,
> Hilmar
>
>
> Hilmar Berger schrieb:
> > 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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