>>>>> "YJ" == Yuan Jian <jayuan2008 at yahoo.com> >>>>> on Wed, 16 Apr 2008 18:42:53 -0700 (PDT) writes: YJ> thanks, YJ> can I ask another basic question? yes, but *NOT* on R-devel. PLEASE! There seems to be a recent tendency to misuse R-devel for things that *REALLY* *ONLY* belong to R-help. [...............]