[R] problems with coercing a factor to be numeric

[D. Rizopoulos]

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.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.
>
>     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/