[BioC] How to boxplot Print tip group intensities with limma, out from marray objects ?

[Giulio Di Giovanni]

Hi guys,

I was trying to have a boxplot of M values by print-tip group starting from 
limma's MAList, but I'm not able to do it.

the only way I found is through marray.

I did

library(limma)
rawset <- read.maimages(source="genepix", ext="gpr")
MAset <- normalizeWithinArrays(rawset, method="none")

# some images from marray

library(convert)
rawmarray <- as(rawset, "marrayRaw")
boxplot(rawmarray[,1], xvar = "maPrintTip", yvar = "maM")


and this it works perfectly. But I would like to have a clean script, 
without recurring to marray.. And  it's also to learn how to do it...

Do someone knows if it is possible, and how to do it ? I guess it is, as 
limma have

plotPrintTipLoess()

for MA plots...

Thanks in advance,

Giulio