[Rd] Package "datasets" not exporting anything on a recent R-2.15.1-patched

[Uwe Ligges]

On 26.08.2012 20:01, Laurent Gautier wrote:
> On 2012-08-26 19:27, Prof Brian Ripley wrote:
>> On 26/08/2012 18:20, Laurent Gautier wrote:
>>> On 2012-08-26 19:03, Prof Brian Ripley wrote:
>>>> On 26/08/2012 17:25, Laurent Gautier wrote:
>>>>> Hi,
>>>>>
>>>>> I just stumbled on the following apparent oddity: the package
>>>>> "datasets"
>>>>> does not appear to export anything out of its namespace:
>>>>>
>>>>>  > ns_datasets <- getNamespace('datasets')
>>>>>  > getNamespaceExports(ns_datasets)
>>>>> character(0)
>>>>>
>>>>> Not the case with other packages (example here with "utils"):
>>>>>  > ns_utils <- getNamespace('utils')
>>>>>  > head(getNamespaceExports(ns_utils))
>>>>> [1] "?"            ".DollarNames" "adist"        "alarm" "apropos"
>>>>> [6] "aregexec"
>>>>>
>>>>> Is this a temporary glitch, or is there something new and specific to
>>>>> "datasets" ?
>>>>
>>>> Not new, been so since R 2.14.0.
>>>>
>>>> The package contains no R code: the only reason it has a namespace is
>>>> that since 2.14.0 all packages must have one.
>>>>
>>>> There are other data-only packages, but not in base R.
>>>>
>>>> Lazy-loaded data has not been part of the namespace for a long time:
>>>> they are directly in the package's environment.  The reason is the
>>>> namespace scoping rules: if the package's datasets were in its
>>>> namespace, they would be found before any other dataset of that name
>>>> by the package's R functions.
>>>>
>>> Thanks for the quick answer and explanations. The last paragraph above
>>> is leaving me with the wish to understand more before I comment on it.
>>> Would you have an example of finding a dataset in a package's namespace
>>> (before a dataset with the same name in an other package further down in
>>> the search path) being a problem ?
>>
>> It does not happen now, but for example MASS contains both datasets
>> and analysis functions and when the datasets were in the namespace you
>> got them before other datasets (e.g. modified versions) of the same name.
>
> I am seeing two ways for datasets to be used:
> A- as internal data for necessary to a function in a package (e.g,
> conversion tables). Not very frequent, from my limited experience.
> B- as example data, used in the documentation. The most frequent usage.
>
> For A/, the user is not expected to modify the data.

In that case, you can provide the data as an object defined within the 
/R directory, for example.


> For B/, the data are typically passed to functions (to use an example
> from MASS, "huber(chem)").

In that case, you do not want to have it in your NAMESPACE, since you 
just pass those data in a function call.

Uwe Ligges



> I thought a bit about it, but still do no see where exactly this would
> be a problem.
>
> An other example available in R is the vector "letters" (in base). It
> can be thought of as a dataset, yet it is
> - in a namespace
>
>  > "letters" %in% getNamespaceExports(getNamespace("base"))
> [1] TRUE
>
> - probably used in the two situations A/ and B/ above.
>
>
>
>
>
>
>>
>>>
>>>
>>> Best,
>>>
>>> Laurent
>>
>>
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel