You could use lapply indeed of sapply:

irisf[,index] <- lapply(irisf[,index], as.factor)
str(irisf)

On Wed, Sep 9, 2009 at 8:06 AM, Petr PIKAL <petr.pikal@precheza.cz> wrote:

> Dear all
>
> I have a simple problem which I thought is easy to solve but what I tried
> did not work. I want to change character variables to factor in data
> frame. It goes easily from factor to character, but I am stuck in how to
> do backwards conversion.
>
> Here is an example
>
> irisf<-iris
> irisf[,2]<-factor(irisf[,2]) # create second factor
>
> str(irisf)
> 'data.frame':   150 obs. of  5 variables:
>  $ Sepal.Length: num  5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...
>  $ Sepal.Width : Factor w/ 23 levels "2","2.2","2.3",..: 15 10 12 11 16 19
> 14 14 9 11 ...
>  $ Petal.Length: num  1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 ...
>  $ Petal.Width : num  0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.2 0.2 0.1 ...
>  $ Species     : Factor w/ 3 levels "setosa","versicolor",..: 1 1 1 1 1 1
> 1 1 1 1 ...
> index<-sapply(irisf, is.factor)
> irisf[,index]<-sapply(irisf[,index], as.character)
>
> str(irisf)
> 'data.frame':   150 obs. of  5 variables:
>  $ Sepal.Length: num  5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...
>  $ Sepal.Width : chr  "3.5" "3" "3.2" "3.1" ...
>  $ Petal.Length: num  1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 ...
>  $ Petal.Width : num  0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.2 0.2 0.1 ...
>  $ Species     : chr  "setosa" "setosa" "setosa" "setosa" ...
>
> I hoped that backwards conversion would be strightforward but...
>
> irisf[,index]<-sapply(irisf[,index], as.factor)
> str(irisf)
> 'data.frame':   150 obs. of  5 variables:
>  $ Sepal.Length: num  5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...
>  $ Sepal.Width : chr  "3.5" "3" "3.2" "3.1" ...
>  $ Petal.Length: num  1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 ...
>  $ Petal.Width : num  0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.2 0.2 0.1 ...
>  $ Species     : chr  "setosa" "setosa" "setosa" "setosa" ...
>
> I want to get both ch columns converted to factor but sapply produces
> character variables (which is documented as it produces matrix or vector)
>
> > R.Version()
> $platform
> [1] "i386-pc-mingw32"
>
> $arch
> [1] "i386"
>
> $os
> [1] "mingw32"
>
> $system
> [1] "i386, mingw32"
>
> $status
> [1] "Under development (unstable)"
>
> $major
> [1] "2"
>
> $minor
> [1] "10.0"
>
> $year
> [1] "2009"
>
> $month
> [1] "07"
>
> $day
> [1] "15"
>
> $`svn rev`
> [1] "48932"
>
> $language
> [1] "R"
>
> $version.string
> [1] "R version 2.10.0 Under development (unstable) (2009-07-15 r48932)"
>
> Regards
> Petr
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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