You can also use droplevels() on your new object (as of R 2.12).
Cheers,
Roman
On Sun, Apr 24, 2011 at 3:42 PM, Christian Parker <cpar...@pdx.edu> wrote:
> You are creating a new object, but the columns that are stored as factors
> are not being 'refactored' so you are retaining the original list of levels.
> To fix this you can use the factor function after you subset
>
> pa2 = subset(pa, influencia=="AID")
> pa2$influencia<-as.factor(pa2$influencia)
>
>
>
> On Apr 24, 2011, at 6:04 AM, Manuel Spínola <mspinol...@gmail.com> wrote:
>
> > Dear list members,
> >
> > I have a question regarding too subsetting a data set in R.
> >
> > I created an object for my data:
> >
> >> pa = read.csv("espec_indic.csv", header = T, sep=",", check.names = F)
> >
> >> levels(pa$influencia)
> > [1] "AID" "AII" "AP"
> >
> > The object has 3 levels for influencia (AP, AID, AII)
> >
> > Now I subset only observations with influencia = "AID"
> >
> >> pa2 = subset(pa, influencia=="AID")
> >
> > but if I ask for the levels of influencia still show me the 3 levels,
> > AP, AID, AII.
> >
> >> levels(pa2$influencia)
> > [1] "AID" "AII" "AP"
> >
> > Why is that?
> >
> > I was thinking that I was creating a new data frame with only AID as a
> > level for influencia.
> >
> > How can I make a complete new object with only the observations for
> > "AID" and that the only level for influencia is indeed "AID"?
> >
> > Best,
> >
> > Manuel
> >
> >
> >
> >
> > --
> > *Manuel Spínola, Ph.D.*
> > Instituto Internacional en Conservación y Manejo de Vida Silvestre
> > Universidad Nacional
> > Apartado 1350-3000
> > Heredia
> > COSTA RICA
> > mspin...@una.ac.cr
> > mspinol...@gmail.com
> > Teléfono: (506) 2277-3598
> > Fax: (506) 2237-7036
> > Personal website: Lobito de río
> > <https://sites.google.com/site/lobitoderio/>
> > Institutional website: ICOMVIS <http://www.icomvis.una.ac.cr/>
> >
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> >
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