On May 3, 2013, at 8:24 AM, jpm miao wrote: > I have a program, when I write > > if(num!=NA) > > it yields an error message. > > However, if I write > > if(is.na(num)==FALSE) > > it works. > > Why doesn't the first statement work? Read the "manual": ?"NA" -- David Winsemius Alameda, CA, USA