I have mapped a few gene symbols to their entrez IDs using:
library(org.Hs.eg.db) info4gene = select(org.Hs.eg.db, symbols, c("ENTREZID"), "ALIAS")
where symbols are the gene names, such as 'NUDT10'.
As below, why are they some gene symbols can map to more than two entrez IDs?
ALIAS ENTREZID NUDT10 53343 NUDT10 170685
Is this usual to have many to many mapping? Is there a way to give only one to one mapping?