Bill, Thanks. So it is as we suspected.
Kind regards, Greg On 5/13/11 11:19 AM, William Dunlap wrote: >> -----Original Message----- >> From: r-help-boun...@r-project.org >> [mailto:r-help-boun...@r-project.org] On Behalf Of Greg Hirson >> Sent: Friday, May 13, 2011 10:58 AM >> To: R-help@r-project.org >> Subject: [R] period in scale parameter of prcomp >> >> Hi all, >> >> Looking at the help file for prcomp and the code in >> stats:::prcomp.default, the scale parameter for the default S3 method >> has a trailing period: it written as >> >> scale. >> >> I assume there is a reason for it (backwards compatibility with S was >> suggested) but I thought I'd ask. > In ancient versions of S you would get an error running > a function like > f <- function(x, plot=TRUE) { if (plot) plot(x, x^2) } > because when it evaluated plot(x,x^2) the object called > 'plot' was a logical vector, not a function. The usual > workaround was to call the argument 'plot.', as in > f <- function(x, plot.=TRUE) { if (plot.) plot(x, x^2) } > You could still call it as > f(x, plot=FALSE) > since tag abbreviations are allowed in function calls. > > Now the 'plot' in the function call 'plot(x,x^2)' is looked > up differently than the 'plot' in 'if(plot)': the former > search keeps going until it finds a function object. Hence > the dot is no longer needed, although it might make you think > about how 'plot' can mean two different things in the same > environment. Older functions still have this dot because > there is no good reason to change them and changing them can > break old code. > > Bill Dunlap > Spotfire, TIBCO Software > wdunlap tibco.com > >> Thanks, >> Greg >> >> -- >> Greg Hirson >> ghir...@ucdavis.edu >> >> Graduate Student >> Agricultural and Environmental Chemistry >> >> 1106 Robert Mondavi Institute North >> One Shields Avenue >> Davis, CA 95616 >> >> ______________________________________________ >> 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. >> -- Greg Hirson ghir...@ucdavis.edu Graduate Student Agricultural and Environmental Chemistry 1106 Robert Mondavi Institute North One Shields Avenue Davis, CA 95616 ______________________________________________ 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.
