[R] ggplot2 - facetting

[Pedro de Barros]

Dear All,

After having overcome the issue of legends (thanks, Thierry, once 
more), I am trying to use facetting, but here also I can not find how 
to do this. I do not want to use qplot, but rather the more flexible 
options. However, it seems I am doing still something pretty stupid, 
because I always get an error, even if it seems I am doing everything 
like the examples.

My code is below.
set.seed(123)
plotdata2<-data.frame(x=rep((1:4),4), y=rep(0.1*(1:4),4), 
group=sample(factor(rep(1:4,rep(4,4)), labels=c('Class1', 'Class2', 
'Class3', 'Class4'))))
plotdata2 <- plotdata2[order(plotdata2[,'group']),]
plot0<-ggplot()
layer1<-layer(data=plotdata2, 
mapping=aes_string(x='x',y='y'),geom='point', stat='identity')
scaleY<-scale_y_continuous()
scaleX <- scale_x_continuous()
Facets<-facet_grid(group ~ .)
plot1<-plot0+layer1 +scaleY + scaleX + facet_grid(group~.)

plot1

I always get the error message:
Error in check_formula(formula, varnames) :
   Formula contains variables not in list of known variables

Thanks for any help you can provide.

Best,
Pedro