Peter & Hadley, thanks for the clarification. The NA=North America example reminds me of a text analysis problem in which "TO" meant "Take Off" for pilots. Of course many text analysis programs toss supposedly low-information words like that! Thanks, Bob
> -----Original Message----- > From: Peter Dalgaard [mailto:[EMAIL PROTECTED] > Sent: Friday, April 04, 2008 12:18 PM > To: Muenchen, Robert A (Bob) > Cc: [EMAIL PROTECTED] > Subject: Re: [R] NA vs. <NA> > > Muenchen, Robert A (Bob) wrote: > > Dear R-Helpers, > > > > Why does R show character missing values in vectors as NA and when > > stored in a data frame as <NA>? I've searched but did not find an > > explanation. > > > > Thanks, > > Bob > > > > > >> gender <- c("f","f","f",NA,"m","m","m","m") > >> gender > >> > > [1] "f" "f" "f" NA "m" "m" "m" "m" #here it lacks brackets. > > > >> q1 <- c(1,2,2,3,4,5,5,4) > >> q1 > >> > > [1] 1 2 2 3 4 5 5 4 > > > >> myDF <- data.frame(q1,gender) > >> myDF > >> > > q1 gender > > 1 1 f > > 2 2 f > > 3 2 f > > 4 3 <NA> #here it has brackets. > > 5 4 m > > 6 5 m > > 7 5 m > > 8 4 m > > > It is actually a factor in the latter case > > > data.frame(gender)$gender > [1] f f f <NA> m m m m > Levels: f m > > However, you have the same effect with > > > data.frame(gender,stringsAsFactors=FALSE) > gender > 1 f > 2 f > 3 f > 4 <NA> > 5 m > 6 m > 7 m > 8 m > > The thing to notice is that the printing is without the quote > character. > We also have > > > noquote(gender) > [1] f f f <NA> m m m m > > And the point in either case is that we need some way to distinguish > between NA (missing) and "NA" (New Alliance, Noradrenalin, North > America, Neil Armstrong, etc.) > > -- > O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B > c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K > (*) \(*) -- University of Copenhagen Denmark Ph: (+45) > 35327918 > ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) > 35327907 > ______________________________________________ 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.
