R help - Oct 2023 - Dynamically create a (convenience) function in a package

Hi,

n a package, I have a data object with attributes, and I want to 
dynamically create a convenience function to access those attributes. 
This way, instead of using attr(x, "number"), I would like to use
number(x).



Because I don't know in advance which attributes the data object may 
have, I've used the following algorithm:

x <- structure(pi, number=exp(1))

a <- attributes(x)

for (n in names(a)) {

   if (!exists(n, mode="function")) {

     f <- eval(parse(text=sprintf("function(x) { attr(x, '%s') }
", n)))


     assign(n, f, envir=.GlobalEnv)

   }

}

number(x)

However, I believe modifying the global environment with this is not 
allowed by CRAN for a package. Is there a way to implement such 
functionality?

Thanks Sigbert

-- 
https://hu.berlin/sk
https://www.stat.de/faqs
https://hu.berlin/mmstat
https://hu.berlin/mmstat-ar

If you don't know the name of the attributes in advance, how can you know
the function name to be able to call it? This seems like a very flawed
approach.

Also, I would discourage the use of eval(parse(text = )), it's almost
always not the right way to do what you want to do. In your case,

eval(bquote(function(x) attr(x, .(n))))

would be better.


On Mon, Oct 30, 2023, 06:28 Sigbert Klinke <sigbert at wiwi.hu-berlin.de>
wrote:
> Hi,
>
> n a package, I have a data object with attributes, and I want to
> dynamically create a convenience function to access those attributes.
> This way, instead of using attr(x, "number"), I would like to use
> number(x).
>
>
>
> Because I don't know in advance which attributes the data object may
> have, I've used the following algorithm:
>
> x <- structure(pi, number=exp(1))
>
> a <- attributes(x)
>
> for (n in names(a)) {
>
>    if (!exists(n, mode="function")) {
>
>      f <- eval(parse(text=sprintf("function(x) { attr(x,
'%s') } ", n)))
>
>
>      assign(n, f, envir=.GlobalEnv)
>
>    }
>
> }
>
> number(x)
>
> However, I believe modifying the global environment with this is not
> allowed by CRAN for a package. Is there a way to implement such
> functionality?
>
> Thanks Sigbert
>
> --
> https://hu.berlin/sk
> https://www.stat.de/faqs
> https://hu.berlin/mmstat
> https://hu.berlin/mmstat-ar
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
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>
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