[R] problems with coercing a factor to be numeric

[Rolf Turner]

Given that your labels are "no" and "yes", what do you expect R to
do?  To quote a well-known fortune, "R is lacking a mind_read() function!"

     cheers,

         Rolf Turner

On 01/23/2013 10:58 PM, Francesco Sarracino wrote:
> 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.rizopoulos at 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.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/
>>
>
>