[R] silently testing for data from another package for .Rd examples

[Yihui Xie]

.packages(all = TRUE) will give you a list of all available packages
without really loading them like require().

Regards,
Yihui
--
Yihui Xie <xieyihui at 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 <friendly at 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
>
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