[BioC] How to determine genes' presence

[Wuming Gong]

Hi, 

I did analysis of some public available microarray data sets
(available as .cel files), then mapped the affymatrix probe IDs to
EnsEMBL ID by EnsMart. I am interested in whether some genes are
present or absent (binary) in given samples. I have a question: if
several different probes reprenting the same gene have the different
P/M/A calls, are there any strategies for determing whether the gene
is present or absent in the sample?

Wuming