A logical operation involving NA returns NA, never TRUE or FALSE: See the 8th Circle of the R Inferno (8.1.4):
http://www.burns-stat.com/pages/Tutor/R_inferno.pdf > num <- 1 > num==NA [1] NA > is.na(num) [1] FALSE ------------------------------------- David L Carlson Associate Professor of Anthropology Texas A&M University College Station, TX 77840-4352 -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of jpm miao Sent: Friday, May 3, 2013 10:25 AM To: r-help Subject: [R] Why can't R understand if(num!=NA)? 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? Thanks, Miao [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
