R help - Jun 2018 - Extract function parameters from a R expression

Hi,

I have read an R program with

expr <- parse("myRprg.R")

How can I extract the parameters of a specifc R command, e.g.
"library"?

So, if myprg.R containes the lines

library("xyz")
library("abc")

then I would like to get "xyz" and "abc" back from expr.

Thanks in advance

Sigbert

-- 
https://hu.berlin/sk

You need to recursively walk the parse tree/AST. See, e.g.,
https://adv-r.hadley.nz/expressions.html#ast-funs

Hadley

On Wed, Jun 20, 2018 at 10:08 AM, Sigbert Klinke
<sigbert at wiwi.hu-berlin.de> wrote:
> Hi,
>
> I have read an R program with
>
> expr <- parse("myRprg.R")
>
> How can I extract the parameters of a specifc R command, e.g.
"library"?
>
> So, if myprg.R containes the lines
>
> library("xyz")
> library("abc")
>
> then I would like to get "xyz" and "abc" back from
expr.
>
> Thanks in advance
>
> Sigbert
>
> --
> https://hu.berlin/sk
>
>
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
http://hadley.nz

... or if the argument is just quoted text or a numeric value as in your
library() example, don't parse the text and use regex's to search for
the
function call and pick out the text of the arguments.

Again, this only works (I think) for the simple sort of case of your
example. Beyond that, you'll have to follow Hadley's prescription.

Cheers,
Bert





Bert Gunter

"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )

On Wed, Jun 20, 2018 at 1:26 AM, Hadley Wickham <h.wickham at gmail.com>
wrote:
> You need to recursively walk the parse tree/AST. See, e.g.,
> https://adv-r.hadley.nz/expressions.html#ast-funs
>
> Hadley
>
> On Wed, Jun 20, 2018 at 10:08 AM, Sigbert Klinke
> <sigbert at wiwi.hu-berlin.de> wrote:
> > Hi,
> >
> > I have read an R program with
> >
> > expr <- parse("myRprg.R")
> >
> > How can I extract the parameters of a specifc R command, e.g.
"library"?
> >
> > So, if myprg.R containes the lines
> >
> > library("xyz")
> > library("abc")
> >
> > then I would like to get "xyz" and "abc" back from
expr.
> >
> > Thanks in advance
> >
> > Sigbert
> >
> > --
> > https://hu.berlin/sk
> >
> >
> >
> > ______________________________________________
> > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide http://www.R-project.org/
> posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>
>
>
> --
> http://hadley.nz
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/
> posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]

If you specifically want to know which packages were loaded by the script
then using a vanilla version of R (i.e. one where only base packages are
loaded):

  vanilla_search <- search()
  source("myRprg.R")
  setdiff(search(), vanilla_search)



On Wed, Jun 20, 2018 at 4:08 AM, Sigbert Klinke
<sigbert at wiwi.hu-berlin.de> wrote:
> Hi,
>
> I have read an R program with
>
> expr <- parse("myRprg.R")
>
> How can I extract the parameters of a specifc R command, e.g.
"library"?
>
> So, if myprg.R containes the lines
>
> library("xyz")
> library("abc")
>
> then I would like to get "xyz" and "abc" back from
expr.
>
> Thanks in advance
>
> Sigbert
>
> --
> https://hu.berlin/sk
>
>
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


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