[R] nlme graphics in a loop problem

[Chris Knight]

Hi, I'm fitting mixed effects models using the lme function of the nlme
package. This involves using the various associated plot functions.
However, when I attempt to fit a number of models using an loop, whilst
the models work, the plot functions fail. As a trivial example, the
following works:

library(nlme)

graphics.off()
x<-c(1:10)
y<-c(1:4,7:12)
b<-as.factor(c(rep("A",5),rep("B",5)))
model<-lme(y~x, random=~1|b)
plot(model)

however the following, identical code in a loop, doesn't:

graphics.off()
for(i in 1:2){
x<-c(1:10)
y<-c(1:4,7:12)
b<-as.factor(c(rep("A",5),rep("B",5)))
model<-lme(y~x, random=~1|b)
plot(model)
}

Mostly this is only inconvenient, since a similar plot may be created
successfully within the loop using plot(fitted(model),resid(model)),
however, I'd be keen to find out whether this is a general problem/sign
of something deeper or I'm just missing something easy that could sort
it out.

Thanks,
Chris
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Dr. Christopher Knight                               Tel:+44 1865 275111
Dept. Plant Sciences                                     +44 1865 275790
South Parks Road
Oxford     OX1 3RB                                   Fax:+44 1865 275074
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