entrez_GeneSets: GeneSet Entrez mapper
Description
This function maps the gene identifiers of a GeneSet object to Entrez identifiers
and returns an error if none of them could be found.
Arguments
gs
GeneSet or SignedGeneSet
Value
GeneSet or SignedGeneSet
Details
gCMAPWeb uses this function to ensure that all submitted / retrieved Entrez Ids
are valid.