[BioC] How to filter genes according to the intensities of both channels for cDNA array?

[Xiao Shi]

Hi everybody,
I am working on 10 GPR files from a time course cDNA array
experiment.Aftersome normalization steps,i got the M and A for 10
arrays.And then i want to apply the quality control procedures to flag 
logratio(M) for those spots to Na whose inteinsities form either channel is 
lower than 200.what can i do?

The procedures i did are as follows:
library(marray)
file=c('2000009478.gpr','2000009471.gpr','2000009472.gpr','2000009473.gpr','
2000009479.gpr','2000009466.gpr','2000009467.gpr','2000009468.gpr','
2000009480.gpr','2000009481.gpr')
target<-read.marrayInfo(fname="e:/gpr/zpz/zpz-target.txt")
##Read probe related information
galinfo<-read.Galfile("GAL-13K.txt",path="e:/gpr/zpz")
##Read expression data
zraw=read.GenePix
(fnames=file,path="e:/gpr/zpz/results",layout=galinfo$layout,gnames=galinfo$gnemes,target=target)

##normalization on print tips
zraw.norm=maNormMain(zraw)

##Between slides normalization
zraw.normg=maNormScale(zraw.norm,norm="g")

##And then the genefilter procedures,
## I want to flag the logratio(M) to NA according to the intensity of both 
channels of a spot,and then select the genes if the 
### sbsolute logratio(|M|) is grater than one.What can i do,what's the code 
doing that?
Thanks in advance.
Shi Jiantao

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