[R-sig-Epi] Transform function
Ralf Finne
Ralf.Finne at syh.fi
Sun Jun 10 22:05:45 CEST 2007
Hi all epidemiologist.
I visited the exellent course SPE in Tartu in May.
One small detail created a question. From www.pubhealth.ku.dk/~bxc/SPE/
I found "A short introduction to R" by Michael Hills, Martyn Plummer and
Bendix
Carstensen.
On page 6 there is an example of the function "transform":
births<- transform(births,hyp=factor(hyp,labels(c("normal","hyper"))))
Running the program:
> library(Epi)
> data(births)
> str(births)
'data.frame': 500 obs. of 8 variables:
$ id : num 1 2 3 4 5 6 7 8 9 10 ...
$ bweight: num 2974 3270 2620 3751 3200 ...
$ lowbw : num 0 0 0 0 0 0 0 0 0 0 ...
$ gestwks: num 38.5 NA 38.2 39.8 38.9 ...
$ preterm: num 0 NA 0 0 0 0 0 0 0 0 ...
$ matage : num 34 30 35 31 33 33 29 37 36 39 ...
$ hyp : num 0 0 0 0 1 0 0 0 0 0 ...
$ sex : num 2 1 2 1 1 2 2 1 2 1 ...
> births<- transform(births,hyp=factor(hyp,labels(c("normal","hyper")))
)
> str(births)
gives:
'data.frame': 500 obs. of 8 variables:
$ id : num 1 2 3 4 5 6 7 8 9 10 ...
$ bweight: num 2974 3270 2620 3751 3200 ...
$ lowbw : num 0 0 0 0 0 0 0 0 0 0 ...
$ gestwks: num 38.5 NA 38.2 39.8 38.9 ...
$ preterm: num 0 NA 0 0 0 0 0 0 0 0 ...
$ matage : num 34 30 35 31 33 33 29 37 36 39 ...
$ hyp : Factor w/ 2 levels "1","2": NA NA NA NA 1 NA NA NA NA NA ...
$ sex : num 2 1 2 1 1 2 2 1 2 1 ...
The item births$hyp is transformed from numeric into a factor in a wrong
way.
The worst thing is that in the beginning in Tartu the transformation was
sometimes
correct and sometimes wrong. Am I doing a mistake or is there a memory
collision in the R system. I have tested on two PC:s with XP on R
versions 2.4.1 and 2.5.0
and Epi package on two versions the newest and an older one.
By the way how do I find the data files included in the Epi-package?
The functions I
find by.
search()
ls(2)
Thank you and good luck with the great work you are doing.
Ralf Finne.
Svenska Yrkeshögskolan
Vasa Finland.
+358 505 539643
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