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

[Uwe Ligges]

Actually it is recommended to test for the availability of a valid 
package with find.package(), particularly in this case where the name of 
the package is already know.

Best,
Uwe



On 24.08.2011 18:29, Yihui Xie wrote:
> .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
>>
>> ______________________________________________
>> R-help at 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 at 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.