I have a specific question in R to ask, in my phenodata, sometimes two chip results are from the same patient, one for primary cancer one for metastasis, I know I can do this to extract all chip results from a specific tissue: exprs(obj)[,which(pData(obj)[,2<or whatever="" number="">]=="liver")] I wonder if there is a way to get all samples from patients with paired samples? I understand this can be done using a database but I think it will be so helpful if I can just do this in R. Best Hao [[alternative HTML version deleted]]