Dear all
I was willing to use argument 'exclude' in function xtabs to remove some
levels of factors (xtabs help page says '"exclude: a vector of values
to be
excluded when forming the set of levels of the classifying factors").
I tried:
> mydata <- data.frame(
+ treatment = c("B", "A", "C", "C",
"B", "B", "C", "A", "B",
"B", NA,
"C"),
+ surv = c("YES", "NO", "YES",
"YES", "NO", "NO", "NO",
"YES", "YES",
"NO", "NO", NA)
+ )
> levels(mydata$treatment)
[1] "A" "B" "C"
> # try to remove level "B" in variable treatment
> xtabs(formula = ~ treatment + surv, data = mydata, exclude = "B")
surv
treatment NO YES
A 1 1
B 3 2
C 1 2
One alternative is to do:
> xtabs(formula = ~ treatment + surv, data = mydata[mydata$treatment !=
"B",
], drop.unused.levels = TRUE)
surv
treatment NO YES
A 1 1
C 1 2
But I don't understand why I cannot remove "B" directly with
argument
exclude.
Any help is welcome
Regards
Matthieu
My version on Windows XP
platform i386-pc-mingw32
arch i386
os mingw32
system i386, mingw32
status
major 2
minor 9.0
year 2009
month 04
day 17
svn rev 48333
language R
version.string R version 2.9.0 (2009-04-17)
------------------
Matthieu Lesnoff
CIRAD
BP 1813, Quartier Niar?la, Immeuble Kouma
Bamako, Mali
E-mail: matthieu.lesnoff at cirad.fr