Thanks for the reply. The solution of requiring the namespace from within Rcpp
hadn't occurred to me.
I had used Environment::namespace_env("pkg_name") before, but I think the
problem here is that lazy-loaded (and maybe other elements we expect in R) are
not available if this is done from Rcpp. E.g.
# (using R --vanilla)
Rcpp::cppFunction('Rcpp::Environment getUnloaded2() { return
Rcpp::Environment::namespace_env("nycflights13"); }')
ls(envir = getUnloaded2())
# empty, whereas the following:
nycflights13::flights
# pulls the data, with the package not being loaded or attached.
To close this thread, I think what the latter command does differently to Rcpp
is to load the package, because sessionInfo() after running the second command,
includes nycflights13 in the section "loaded via a namespace (and not
attached):" This is not the case after pulling the environment into an Rcpp
variable.
Thanks again for steering me,
Jack
On 04/15/2018 10:18 PM, Kevin Ushey wrote:
> The environments called 'package:foo' are associated with attached packages;
> that is, they're located on the search path. You likely want to find the
> actual package namespace.
>
> I think we have a static function Environment::namespace_env() for this. Or
> you can just call back to R with requireNamespace().
>
> Kevin
>
> On Fri, Apr 13, 2018 at 10:10 PM, Wasey, Jack O <[email protected]
> <mailto:[email protected]>> wrote:
>
> Dear all,
>
> It seems I can reference lazy-loaded data from an unloaded, unattached
> package from R, but not using the equivalent Rcpp as described in the
> quickref document. I checked out:
> http://dirk.eddelbuettel.com/code/rcpp/html/Environment_8h_source.html
> <http://dirk.eddelbuettel.com/code/rcpp/html/Environment_8h_source.html> and
> even the scant references to environments in the C API section of "Writing R
> Extensions" and doesn't see what I'm missing. I suspect this is a limitation
> of R's C interface, not necessarily Rcpp itself.
>
> I use the package nycflights13 as an example. Running `sessionInfo()`
> shows the package nycflights13 is not loaded, then I run:
> R --vanilla
> > a <- nycflights13::flights
>
> Which completes without error. In Rcpp, I cannot even get a handle on the
> package namespace if it is not loaded.
>
> Rcpp::cppFunction('Rcpp::Environment getUnloaded() { Rcpp::Environment
> env("package:nycflights13"); return env;}')
> getUnloaded()
> Error in getUnloaded() :
> Cannot convert object to an environment: [type=character;
> target=ENVSXP].
>
> library(nycflights13)
> Rcpp::cppFunction('Rcpp::Environment getUnloaded() { Rcpp::Environment
> env("package:nycflights13"); return env;}')
> getUnloaded()
> <environment: package:nycflights13>
> attr(,"name")
> [1] "package:nycflights13"
> attr(,"path")
> [1]
> "/Library/Frameworks/R.framework/Versions/3.4/Resources/library/nycflights13"
> >
>
> I also found that simple using `loadNamespace` was insufficient for the
> Rcpp approach to work, but after `library` or `attachNamespace` the above
> function does work.
>
> Am I treading in another rare code path? All I want to do is use a
> lazy-loaded data set in an Rcpp function when the package may not be loaded
> when called. Should I just be passing it as a parameter to the function? This
> seems ugly.
>
> Using Rcpp 0.12.16, R 3.4.3 on Mac.
>
> Any advice appreciated. Thanks,
>
> Jack
>
>
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