R help - May 2013 - lazy loading like object

Dear List,


I'm writing the package MODIS (currently on R-forge), I lazy load some data
which is a very elegant solution. These lazy loaded objects are typically used
inside functions, most of that objects are not directly used by users. One of
the objects I want to lazy load (is a result of a function) has the problem that
it can only be generated having an external library (gdal-bin) installed. This
installation enables _some_ (important) functionality in the package.
The problem is that to generate this object it takes some time (on Linux less
than 2 sec on windows 5 and more). I can not provide this object within the
package source code (ie as RData) as I'm not sure if it is the same on every
Hardware/Software environment.


I think there are several imaginable solutions (that I can't solve by my
own).
One is to hide it for the R CMD check and INSTALL process? (This would be a
solution as the object is only needed inside functions already enabled by
gdal-bin)
To generate the object and send it to the package environment...(I don't
know how)


Basically I'm aiming at a object loaded
_once_after_the_check_of_the_availability_ of the external library gdal-bin. So
it takes only _once_ the time to produce that object that is from now on
available for any other function in the package environment.


I hope I was clear, thanks in advanced,
Matteo Mattiuzzi

1) This is a topic for the R-devel list.

2) It sounds like something which should be done at installation, and 
can easily be done via top-level code in your R files.

3) We have no idea what 'gdal-bin' is, nor how that can be a
'library'.
  But save()-d R objects are portable unless something like external 
pointers are involved (when they cannot be saved properly).

On 28/05/2013 08:20, Matteo Mattiuzzi wrote:
> Dear List,
>
>
> I'm writing the package MODIS (currently on R-forge), I lazy load some
data which is a very elegant solution. These lazy loaded objects are typically
used inside functions, most of that objects are not directly used by users. One
of the objects I want to lazy load (is a result of a function) has the problem
that it can only be generated having an external library (gdal-bin) installed.
This installation enables _some_ (important) functionality in the package.
> The problem is that to generate this object it takes some time (on Linux
less than 2 sec on windows 5 and more). I can not provide this object within the
package source code (ie as RData) as I'm not sure if it is the same on every
Hardware/Software environment.
>
>
> I think there are several imaginable solutions (that I can't solve by
my own).
> One is to hide it for the R CMD check and INSTALL process? (This would be a
solution as the object is only needed inside functions already enabled by
gdal-bin)
> To generate the object and send it to the package environment...(I
don't know how)
>
>
> Basically I'm aiming at a object loaded
_once_after_the_check_of_the_availability_ of the external library gdal-bin. So
it takes only _once_ the time to produce that object that is from now on
available for any other function in the package environment.
>
>
> I hope I was clear, thanks in advanced,
> Matteo Mattiuzzi

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
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