I used the
AnnotationDbi::mapIds function over the
EnsDb.Mmusculus.v79 package to map Ensembl Gene IDs back to entrez id over a a long vector of ENSG Ids.
I expected this to return a 1:1 mapping when
mapIds(..., multiVals='first'), but was surprised that this returned several entrez ids concatenated with ";" for a given ensembl gene id, for instance:
R> mapIds(EnsDb.Mmusculus.v79, 'ENSMUSG00000079658', 'ENTREZID', 'GENEID') ENSMUSG00000079658 "67923;102642819"
I've long been working under the assumption that the
multiVals parameter is meant to control this, and it should only return a single identifier when the appropriate value for that parameter is passed (like
I must say, this finding has shaken the bedrock of all things I thought to be true and I'm having a deja vu moment back to 1999 where I'm asking myself again if I actually might be living inside of The Matrix.
Can I get an assist? Thanks :-)
I'm running on the latest bioc, but just to orient ourselves a bit, here some versions of the relevant packages:
EnsDb.Mmusculus.v79_2.1.0 ensembldb_2.0.1 AnnotationDbi_1.38.0