[R] Data frame referencing?

[Sander Oom]

Dear Gabor and Dimitris,

Simple, once you know! It is these little exceptions on the R notation
that get me stuck. Now I am on the loose again!

Thanks,

Sander.

Dimitris Rizopoulos wrote:
> you need to use quotes, i.e.,
> 
> a[a$y > 0.5, "y"] <- 1
> 
> you can also use
> 
> a$y[a$y > 0.5] <- 1
> 
> 
> I hope it helps.
> 
> Best,
> Dimitris
> 
> ----
> Dimitris Rizopoulos
> Ph.D. Student
> Biostatistical Centre
> School of Public Health
> Catholic University of Leuven
> 
> Address: Kapucijnenvoer 35, Leuven, Belgium
> Tel: +32/(0)16/336899
> Fax: +32/(0)16/337015
> Web: http://med.kuleuven.be/biostat/
>      http://www.student.kuleuven.be/~m0390867/dimitris.htm
> 
> 
> ----- Original Message ----- 
> From: "Sander Oom" <slist at oomvanlieshout.net>
> To: <r-help at stat.math.ethz.ch>
> Sent: Friday, August 04, 2006 1:48 PM
> Subject: [R] Data frame referencing?
> 
> 
>> Dear R users,
>>
>> When you do:
>>> x <- rnorm(10)
>>> y <- rnorm(10)
>>> z <- rnorm(10)
>>> a <- data.frame(x,y,z)
>>> a$x
>> [1]  1.37821893  0.21152756 -0.55453182 -2.10426048 -0.08967880 
>> 0.03712110
>> [7] -0.80592149  0.07413450  0.15557671  1.22165341
>>
>> Why does this not work:
>>> a[a$y>0.5,y] <-1
>> Error in "[<-.data.frame"(`*tmp*`, a$y > 0.5, y, value = 1) :
>>        only 0's may be mixed with negative subscripts
>>
>> While this works:
>>> a[a$y>0.5,2] <-1
>>> a
>>             x          y          z
>> 1   1.37821893 -1.0887363  1.7340522
>> 2   0.21152756 -0.7256467 -1.3165373
>> 3  -0.55453182  1.0000000 -2.1116072
>> 4  -2.10426048 -0.4898596 -1.5863823
>> 5  -0.08967880  1.0000000 -0.9139706
>> 6   0.03712110  1.0000000 -1.3004970
>> 7  -0.80592149 -0.7004193 -0.1958059
>> 8   0.07413450  1.0000000 -1.3574303
>> 9   0.15557671 -0.3335407 -2.1991236
>> 10  1.22165341  1.0000000 -0.7576708
>>
>> For a complex loop I would prefer to reference the right colomn by 
>> name,
>> not by number! Now, when the colomns change, I need to check my code 
>> to
>> make sure that the right colomns are referenced.
>>
>> Suggestions much appreciated!
>>
>> Thanks in advance,
>>
>> Sander.
>>
>> ______________________________________________
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>> http://www.R-project.org/posting-guide.html
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>>
> 
> 
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> ______________________________________________
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