[R] problems with coercing a factor to be numeric
d.rizopoulos at erasmusmc.nl
Wed Jan 23 10:53:03 CET 2013
pp <- rep(0:1, 10)
pp <- factor(pp, levels=(0:1), labels=c("no","yes"))
unclass(pp) - 1
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?
> However, whatever I do, I get "Warning message: NAs introduced by coercion"
> and the output is a vector of NA.
> Any ideas?
> On 23 January 2013 10:39, D. Rizopoulos <d.rizopoulos at erasmusmc.nl
> <mailto:d.rizopoulos at erasmusmc.nl>> wrote:
> Check R FAQ 7.10: How do I convert factors to numeric?
> I hope it helps.
> 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
> > 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
> > 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.
Department of Biostatistics
Erasmus University Medical Center
Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
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