[R] Extract function parameters from a R expression

[Bert Gunter]

... 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 using 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 using 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 using 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 using 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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