[Rd] How to (appropropriately) use require in a package?

Prof Brian Ripley ripley at stats.ox.ac.uk
Fri Aug 8 08:47:33 CEST 2014

The safe, elegant way to do this is to use namespace scoping: it is 
still not at all clear why 'other code' needs PkgB *on the search path*.

In other cases seen in CRAN submissions, 'other code' has been in PkgA's 
namespace, and hence things in PkgB's exports have been visible as it 
was imported by PkgA and hence in the environment tree for functions in 
PkgA.  Then namespace scoping will ensure that PkgB's namespace is 
loaded on the cluster workers.

On 08/08/2014 00:58, Joshua Wiley wrote:
> Someone kindly pointed out that it is not clear from my email why Depends
> will not work.  A more complete example is:
> PkgA:
> f <- function(ncores) {
>    cl <- makeCluster(ncores)
>    clusterEvalQ(cl, {
>      require(PkgB)
>    })
>    [other code]
>    ### this is the code I want to work and need to be able to call
>    ### PkgB functions on each of the cluster slaves
>    output <- parLapply(cl, 1:n, function(i) {
>      [code from my package and using some functions from PkgB]
>    })
> }
> As far as I know, just because I add PkgB to the Depends (or imports,
> whatever) of PkgA, does not mean that the cluster started by PkgA will
> automatically have PkgB loaded and functions available.
> Thanks!
> On Fri, Aug 8, 2014 at 9:35 AM, Joshua Wiley <jwiley.psych at gmail.com> wrote:
>> Dear All,
>> What is the preferred way for Package A, to initialize a cluster, and load
>> Package B on all nodes?
>> I am writing a package that parallelizes some functions through the use of
>> a cluster if useRs are on a Windows machine (using parLapply and family).
>>   I also make use of another package in some of my code, so it is necessary
>> to load the required packages on each slave once the cluster is started.
>> Right now, I have done this, by evaluating require(packages) on each
>> slave; however, Rcmd check has a note that I should remove the "require" in
>> my code.
>> Thanks!
>> Josh
>> --
>> Joshua F. Wiley
>> Ph.D. Student, UCLA Department of Psychology
>> http://joshuawiley.com/
>> Senior Analyst, Elkhart Group Ltd.
>> http://elkhartgroup.com
>> Office: 260.673.5518

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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