[Rd] no visible binding for global variable for data sets in a package

[Martin Maechler]

>>>>> Michael Friendly <friendly at yorku.ca>
>>>>>     on Tue, 26 Aug 2014 17:58:34 -0400 writes:

    > I'm updating the Lahman package of baseball statistics to the 2013 
    > release. In addition to
    > the main data sets, the package also contains several convenience 
    > functions that make use
    > of these data sets.  These now trigger the notes below from R CMD check 
    > run with
    > Win builder, R-devel.  How can I avoid these?

    > * using R Under development (unstable) (2014-08-25 r66471)
    > * using platform: x86_64-w64-mingw32 (64-bit)
    > ...
    > * checking R code for possible problems ... NOTE
    > Label: no visible binding for global variable 'battingLabels'
    > Label: no visible binding for global variable 'pitchingLabels'
    > Label: no visible binding for global variable 'fieldingLabels'
    > battingStats: no visible binding for global variable 'Batting'
    > battingStats: no visible global function definition for 'mutate'
    > playerInfo: no visible binding for global variable 'Master'
    > teamInfo: no visible binding for global variable 'Teams'

    > One such function:

    > ## function for accessing variable labels

    > Label <- function(var, labels=rbind(battingLabels, pitchingLabels, 
    > fieldingLabels)) {
    > wanted <- which(labels[,1]==var)
    > if (length(wanted)) labels[wanted[1],2] else var
    > }

and you are using the data sets you mentioned before,
(and the checking has been changed recently here).

This is a bit subtle:
Your data sets are part of your package (thanks to the default
lazyData), but *not* part of the namespace of your package.
Now, the reasoning goes as following: if someone uses a function
from your package, say Label() above, 
by
	Lahman::Label(..)
and your package has not been attached to the search path,
your user will get an error, as the datasets are not found by
Label().

If you consider something like   Lahman::Label(..)
for a bit and the emphasis we put on R functions being the
primary entities, you can understand the current, i.e. new, 
R CMD check warnings.

I see the following two options for you:

1) export all these data sets from your NAMESPACE
   For this (I thinK), you must define them in  Lahman/R/ possibly via a 
   Lahman/R/sysdata.rda

2) rewrite your functions such that ensure the data sets are
   loaded when they are used.


"2)" actually works by adding    
   	stopifnot(require(Lahman, quietly=TRUE))
  as first line in Label() and other such functions.

It works in the sense that  Lahman::Label("yearID")  will
work even when Lahman is not in the search path,
but   R-devel CMD check   will still give the same NOTE,
though you can argue that that note is actally a "false positive".
   
Not sure about another elegant way to make "2)" work, apart from
using  data() on each of the datasets inside the
function.  As I haven't tried it, that may *still* give a
(false) NOTE..

This is a somewhat interesting problem, and I wonder if everyone
else has solved it with '1)' rather than a version of '2)'.

Martin