This is an old one. NA is not a real value, but a marker of something missing. Hence the expression
a == NA is really an incomplete expression (the right hand side of the equality is missing) and hence cannot be evaluated. Hence the error message. This is why the function is.na() exists, essentially. There are a number of elegant solutions. Take an exampel > x <- 1:5 > is.na(x[3]) <- TRUE ## the preferred way to set NA s > x [1] 1 2 NA 4 5 > sum(x, na.rm = TRUE) [1] 12 alternatively: > x[is.na(x)] <- 0 > x [1] 1 2 0 4 5 > sum(x) ## probably what you were headed [1] 12 > Bill Venables CSIRO Laboratories PO Box 120, Cleveland, 4163 AUSTRALIA Office Phone (email preferred): +61 7 3826 7251 Fax (if absolutely necessary): +61 7 3826 7304 Mobile: +61 4 8819 4402 Home Phone: +61 7 3286 7700 mailto:[EMAIL PROTECTED] http://www.cmis.csiro.au/bill.venables/ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Keld Jørn Simonsen Sent: Friday, 4 July 2008 4:30 PM To: r-help@r-project.org Subject: [R] problem with NA and if Hi I would like to sum a number of time series, some of them having NA's Standard action is here that if I sum a value with a NA, then the result is NA. I would like it to just keep the value. I then try to: a = NA; if (a == NA) { a = 0} just to try it out, but it says Error in if (a == NA) { : missing value where TRUE/FALSE needed What is wrong, and can I do it smarter? I looked at na.action but I don't see how it affects addition of vectors, nor time series. Best regards keld ______________________________________________ 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.
