Dear Brian (and Gabor), Thanks -- that makes sense.
John -------------------------------- John Fox, Professor Department of Sociology McMaster University Hamilton, Ontario Canada L8S 4M4 905-525-9140x23604 http://socserv.mcmaster.ca/jfox -------------------------------- > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Prof Brian Ripley > Sent: Wednesday, May 09, 2007 12:05 PM > To: John Fox > Cc: r-devel@r-project.org > Subject: Re: [Rd] Behaviour of read.table with empty columns > > On Wed, 9 May 2007, John Fox wrote: > > > Dear r-devel list members, > > > > I stumbled across the following behaviour of read.table() recently: > Suppose > > that I have the data > > > > a " " "" > > "" "" "" > > > > in a file or copied to the clipboard, and issue the command > > > >> DF <- read.table("clipboard") > >> DF > > V1 V2 V3 > > 1 a NA NA > > 2 NA NA > > > >> is.na(DF) > > V1 V2 V3 > > [1,] FALSE TRUE TRUE > > [2,] FALSE TRUE TRUE > > > > I was surprised by the NAs. Note that they occur only when a column > > consists entirely of empty strings or strings composed of blanks. > > > > On the other hand > > > >> data.frame(A=c("", "", "")) > > A > > 1 > > 2 > > 3 > > > > works as I would have expected. > > How did you expect R to know that "" meant a character > column? You are allowed to quote any type of column, so as > far as read.table is concerned the columns is entirely empty > and so its type is unknown. It defaults to the simplest > possible type, logical. > > The answer is I think to use colClasses="character". > > It is probably slightly more accurate to say that if > colClasses is not given, all columns are read as character > columns, and then converted to the simplest possible type. > In earlier versions of R you could get NULL columns (if there > were no rows at all), but now the simplest is logical. > > Brian > > > A work-around for me was > > > >> DF[is.na(DF)] <- "" > >> DF > > V1 V2 V3 > > 1 a > > 2 > > > > But, as I said, I found the behaviour of read.table() puzzling. > > > > All this is with R 2.5.0 on a Windows XP Pro SP 2 system. > > > > Comments? > > > > Thanks, > > John > > > > -------------------------------- > > John Fox, Professor > > Department of Sociology > > McMaster University > > Hamilton, Ontario > > Canada L8S 4M4 > > 905-525-9140x23604 > > http://socserv.mcmaster.ca/jfox > > > > ______________________________________________ > > R-devel@r-project.org mailing list > > https://stat.ethz.ch/mailman/listinfo/r-devel > > > > -- > Brian D. Ripley, [EMAIL PROTECTED] > Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ > University of Oxford, Tel: +44 1865 272861 (self) > 1 South Parks Road, +44 1865 272866 (PA) > Oxford OX1 3TG, UK Fax: +44 1865 272595 > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
