Thank you all, a few ideas worked perfectly for me. I take "with(dat1,aggregate(B,by=list(A=A),length))" for my task. Have a nice day. Mat -- View this message in context: http://r.789695.n4.nabble.com/Count-cell-Count-by-her-frequency-tp4652650p4652678.html Sent from the R help mailing list archive at Nabble.com.