[R-pkg-devel] sf subsetting with square bracket

[Duncan Murdoch]

On 03/02/2019 5:21 p.m., Berry Boessenkool wrote:
> 
> Hi,
> my package in question can only be online next week, but here's a script 
> for a MWE:
> https://gist.github.com/brry/7728b9b2d35afad7f1fc5978c3315009
> The script uses devtools and osmplotr to
> - create a package with a bare minimum dummy function
> - run the code showing the problem
> - create a solution using the ::: import
> - clean up, removing the package and the folder for it

Thanks.  I can confirm the issue.  I think the problem is that neither 
your sample package nor osmplotr declares a dependency on sf, and it is 
not loaded.  I don't know if it makes sense for your package to do so, 
but osmplotr probably should, since it is creating "sf" objects.

If I force sf to be loaded by changing your dummy function to

dummy <- function(map,obj)
{
   requireNamespace("sf")
   add_osm_objects(map, obj[1:10,], col='green')
}

then things are fine.  In your real package, you'll want to be prepared 
to handle the case where "sf" is not installed.

sf is a big package, so maybe it's intentional to not require it.  I 
don't know these packages at all, but it seems to me that if osmplotr is 
returning objects of class "sf", then it should probably make sure that 
the "sf" package is loaded so that methods can be found.

Duncan Murdoch


> 
> btw:  sf 0.7.2,   R 3.4.3,   x86_64-w64-mingw32/x64 (64-bit)
> *
> *
> Kind regards,
> Berry
> 
> 
> ------------------------------------------------------------------------
> *From:* Duncan Murdoch <murdoch.duncan using gmail.com>
> *Sent:* Sunday, February 3, 2019 21:41
> *To:* Berry Boessenkool; R package devel
> *Subject:* Re: [R-pkg-devel] sf subsetting with square bracket
> On 03/02/2019 3:02 p.m., Berry Boessenkool wrote:
>> 
>> Hi,
>> 
>> if sf is not loaded, subsetting an sf object with square brackets loses the sf class in the geometry column:
>> sfobj[somerows,]
>> For usage in a package, I do not want to call library(sf) first.
>> 
>> [ is an S3 method in sf:
>> https://github.com/r-spatial/sf/blob/master/NAMESPACE#L6
>> https://github.com/r-spatial/sf/blob/master/R/sf.R#L299
>> 
>> In my package (with an sf object from osmplotr), using
>> sf:::"[.sf"(obj, somerows, allcolumns)
>> works fine, but of course Rcmd check complains about the Unexported object imported by a ':::' call.
>> 
>> How can I use the sf [ method without completely loading sf?
>> (and also without depending on dplyr::select)
>> 
>> I guess I'm missing some really clever method import.
>> Can someone point me in the right direction?
> 
> You need to show us something reproducible if you want help.  Is your
> package on Github or some other public repository?
> 
> Duncan Murdoch