Thanks,
this works! but I am surprised that R has such a strange behavior and that
there is no way to control it.
BTW, also as.integer(pp)-1 works!
Still, it doesn't look to me as a first best.
At any rate, thanks a lot for your help.
f.
On 23 January 2013 10:53, D. Rizopoulos <d.rizopou...@erasmusmc.nl> wrote:
> check also
>
> pp <- rep(0:1, 10)
> pp <- factor(pp, levels=(0:1), labels=c("no","yes"))
>
> unclass(pp)
> unclass(pp) - 1
>
>
> Best,
> Dimitris
>
>
> On 1/23/2013 10:48 AM, Francesco Sarracino wrote:
> > Dear Dimitris,
> >
> > thanks for your quick reply. I've tried the solutions proposed in 7.10
> > How do I convert factors to numeric?
> >
> > as.numeric(as.character(pp))
> > and
> > as.numeric(levels(pp))[as.integer(pp)]
> >
> > However, whatever I do, I get "Warning message: NAs introduced by
> coercion"
> > and the output is a vector of NA.
> >
> > Any ideas?
> > f.
> >
> >
> >
> > On 23 January 2013 10:39, D. Rizopoulos <d.rizopou...@erasmusmc.nl
> > <mailto:d.rizopou...@erasmusmc.nl>> wrote:
> >
> > Check R FAQ 7.10: How do I convert factors to numeric?
> >
> >
> > I hope it helps.
> >
> > Best,
> > Dimitris
> >
> >
> > On 1/23/2013 10:33 AM, Francesco Sarracino wrote:
> > > Dear R listers,
> > >
> > > I am trying to compute the mean of a dummy variable that is
> > encoded as a
> > > factor. However, even though the levels of my factor are 0 - 1,
> > when I
> > > compute the mean (after coercing the factor to be
> > > numeric), R changes 0 into 1 and 1 into yes, thus altering my
> > expected
> > > result.
> > >
> > > Please, consider the following working example:
> > > pp <- rep(0:1, 10)
> > > pp <- factor(pp, levels=(0:1), labels=c("no","yes"))
> > > mean(pp) #this won't work because the argument is not numeric or
> > logical
> > > mean(as.integer(pp)) # this computes the average, but not on the
> > range 0-1,
> > > but 1-2. Indeed, the result is 1.5 and not 0.5 as expected.
> > >
> > > What am I doing wrong?
> > > Thanks in advance for your kind support,
> > > f.
> > >
> > >
> >
> > --
> > Dimitris Rizopoulos
> > Assistant Professor
> > Department of Biostatistics
> > Erasmus University Medical Center
> >
> > Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
> > Tel: +31/(0)10/7043478 <tel:%2B31%2F%280%2910%2F7043478>
> > Fax: +31/(0)10/7043014 <tel:%2B31%2F%280%2910%2F7043014>
> > Web: http://www.erasmusmc.nl/biostatistiek/
> >
> >
> >
> >
> > --
> > Francesco Sarracino, Ph.D.
> > https://sites.google.com/site/fsarracino/
>
> --
> Dimitris Rizopoulos
> Assistant Professor
> Department of Biostatistics
> Erasmus University Medical Center
>
> Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
> Tel: +31/(0)10/7043478
> Fax: +31/(0)10/7043014
> Web: http://www.erasmusmc.nl/biostatistiek/
>
--
Francesco Sarracino, Ph.D.
https://sites.google.com/site/fsarracino/
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