This function is design to be used with applyCdfGroups()
on an Affymetrix Mapping (SNP) CDF list structure.
cdfAddProbeOffsets(groups, ...)list structure with groups.
Each group must contain the fields tbase, and expos.
list structure with half the number of groups as the
groups argument (since allele A and allele B groups have
been joined).
applyCdfGroups().