.packages(all = TRUE) will give you a list of all available packages without really loading them like require().
Regards, Yihui -- Yihui Xie <xieyi...@gmail.com> Phone: 515-294-2465 Web: http://yihui.name Department of Statistics, Iowa State University 2215 Snedecor Hall, Ames, IA On Wed, Aug 24, 2011 at 9:28 AM, Michael Friendly <frien...@yorku.ca> wrote: > In an .Rd example for a package, I want to use data from another package, > but avoid loading the entire > package and avoid errors/warnings if that other package is not available. > > If I don't care about loading the other package, I can just do: > > if (require("ElemStatLearn", quietly=TRUE)) { > data(prostate) > # rest of example > } > > I'd rather just be able to do something like: > > if (data(prostate, package="ElemStatLearn")) { > # rest of example > } > > but it appears that data() doesn't return anything useful (like FALSE or > NULL) in case the named data > set doesn't exist, or the package cannot be found. Below are some test > cases in a fresh R 2.13.1 session. > > Is there someway I can incorporate such a data example silently without > errors or warnings if the > package doesn't exist, as is the case with require()? > >> data(prostate, package="ElemStatLearn") >> dd <- data(prostate, package="ElemStatLearn") >> dd > [1] "prostate" >> dd2 <- data(xxxxx, package="ElemStatLearn") > Warning message: > In data(xxxxx, package = "ElemStatLearn") : data set 'xxxxx' not found >> dd2 > [1] "xxxxx" >> dd2 <- data(xxxxx, package="ElemStatLearn", verbose=FALSE) > Warning message: > In data(xxxxx, package = "ElemStatLearn", verbose = FALSE) : > data set 'xxxxx' not found >> >> dd3 <- data(zzzzz, package="foobar") > Error in find.package(package, lib.loc, verbose = verbose) : > there is no package called 'foobar' >> dd3 > Error: object 'dd3' not found >> > > try() doesn't seem to help here: > >> ddtry <- try(data(zzzzz, package="foobar")) > Error in find.package(package, lib.loc, verbose = verbose) : > there is no package called 'foobar' >> ddtry > [1] "Error in find.package(package, lib.loc, verbose = verbose) : \n there > is no package called 'foobar'\n" > attr(,"class") > [1] "try-error" >> > > -- > Michael Friendly Email: friendly AT yorku DOT ca > Professor, Psychology Dept. > York University Voice: 416 736-5115 x66249 Fax: 416 736-5814 > 4700 Keele Street Web: http://www.datavis.ca > Toronto, ONT M3J 1P3 CANADA > > ______________________________________________ > 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.
