[R-pkg-devel] referring to a package data object by two names

Dear R colleagues,

I have a set of versioned data objects in a package. Let's call them

landmarks.2016
landmarks.2017

I need to have access to both of these objects for different calculations both internal to the package and for end users. The objects are saved as rda files in the package's data folder.

I would also like to define an object ? an alias if you will ? that contains the *current* landmarks. This is useful so that some package functions and external scripts do not require editing when the default object changes.

For this, somewhere in the package, I would like to do something like:

# set the current default landmarks
landmarks <- landmarks.2017

I cannot figure out a place to do this in my package because check always complaints that landmarks.2017 does not exist ? I guess lazy loading can only happen after all the R code is evaluated.

* Can anyone suggest a workaround that does not involve saving a third redundant rda object into the package's data folder?

I have placed a toy example package on GitHub:

   https://github.com/jefferis/testdataalias

With many thanks,

Greg Jefferis.

--
Gregory Jefferis, PhD
Division of Neurobiology
MRC Laboratory of Molecular Biology
Francis Crick Avenue
Cambridge Biomedical Campus
Cambridge, CB2 OQH, UK

http://www2.mrc-lmb.cam.ac.uk/group-leaders/h-to-m/g-jefferis
http://jefferislab.org
http://www.zoo.cam.ac.uk/departments/connectomics

Do any of the suggestions in section 1.5.3 of Writing R Extensions "Load hooks" work?

On 9 Oct 2017, at 13:36, Berry Boessenkool <berryboessenkool at hotmail.com> wrote:


Another approach, maybe overkill / not thought through:

latestLandmark <- function()
 {
 files <- dir(file.path(system.file(package="yourpackage"), "data"), 
              pattern="landmark", full.names=TRUE)
 env <- environment()
 dataset <- load(tail(files, 1), envir=env)
 return(invisible(get(dataset, envir=env)))
 }

landmark <- latestLandmark()


Regards,
Berry


From: R-package-devel <r-package-devel-bounces at r-project.org <mailto:r-package-devel-bounces at r-project.org>> on behalf of Gregory Jefferis <jefferis at gmail.com <mailto:jefferis at gmail.com>>
Sent: Sunday, October 8, 2017 14:45
To: Michael Dewey
Cc: r-package-devel at r-project.org <mailto:r-package-devel at r-project.org>
Subject: Re: [R-pkg-devel] referring to a package data object by two names
 
Dear Michael,

Many thanks for writing.

Do any of the suggestions in section 1.5.3 of Writing R Extensions "Load hooks" work?

I thought I had tried all the various permutations in .onLoad but at your prompting I tried some more and this seems to work:

.onLoad <- function (libname, pkgname) {
  # set up default landmarks object
  assign('landmarks',
         envir = parent.env(environment()),
         testdataalias::landmarks.2017)

}

It doesn't seem to tickle R CMD check, but I'm not yet convinced that it is 100% safe. Any comments either way are welcome!

Best wishes,

Greg.