[R] getting arg names in function calls?

[William Dunlap]

> I don't see how that solves
> the example I gave of extracting "plot(x=0, y=1)" from tstFn <-
> function()plot(0, 1).

Try
    > match.call(definition=plot, call=body(tstFn))
    plot(x = 0, y = 1)

plot() is not a great example, since some of its methods do not have an
argument called 'y' (e.g., plot.stepfun) and it has a lot of ... arguments which
you need to go to the help file for.

Bill Dunlap
TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: Spencer Graves [mailto:spencer.graves at structuremonitoring.com]
> Sent: Tuesday, April 08, 2014 4:53 PM
> To: William Dunlap; R list
> Subject: Re: [R] getting arg names in function calls?
> 
> Hi, Bill:
> 
> 
>        Thanks for the reply.  Unfortunately, I don't see how that solves
> the example I gave of extracting "plot(x=0, y=1)" from tstFn <-
> function()plot(0, 1).
> 
> 
>        As I noted, body(tstFn) returns "plot(0, 1)" as an "language"
> object of class "call".  My challenge is to convert that into something
> similar, with explicit names for the arguments.
> 
> 
>        Any thoughts?
>        Spencer
> 
> 
> On 4/7/2014 3:18 PM, William Dunlap wrote:
> > Look at match.call().  E.g.,
> >    > f <- function(x, y = log2(x), ...) match.call()
> >    > f()
> >    f()
> >    > f(1, x=2, anotherArg=3, 4)
> >    f(x = 2, y = 1, anotherArg = 3, 4)
> > or, using its 'definition' and 'call' arguments directly
> >    > match.call(function(x, y, ...)NULL, quote(foo(1, x=2, extraArg=3, 4)))
> >    foo(x = 2, y = 1, extraArg = 3, 4)
> >    > match.call(function(x, y, ...)NULL, quote(foo(1, x=2, extraArg=3, 4)),
> expand.dots=FALSE)
> >    foo(x = 2, y = 1, ... = list(extraArg = 3, 4))
> >
> > Bill Dunlap
> > TIBCO Software
> > wdunlap tibco.com
> >
> >
> >> -----Original Message-----
> >> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
> Behalf
> >> Of Spencer Graves
> >> Sent: Monday, April 07, 2014 3:05 PM
> >> To: R list
> >> Subject: [R] getting arg names in function calls?
> >>
> >>         How can I convert "plot(0, 1)" into "plot(x=0, y=1)"?
> >>
> >>
> >>         More generally, how can I get argument names assigned to function
> >> calls in "language" objects?
> >>
> >>
> >>         Example:
> >>
> >>
> >> tstFn <- function()plot(0, 1)
> >> bo <- body(tstFn)
> >>
> >>
> >> tstFnxy <- function()plot(x=0, y=1)
> >> boxy <- body(tstFnxy)
> >>
> >>
> >>         Is there a function that will modify "bo" to match "boxy"?
> >>
> >>
> >>         My current solution requires me to know the names of the
> >> arguments for "plot" (in this example).  I'd prefer a more general
> >> solution.
> >>
> >>
> >>         Thanks,
> >>         Spencer
> >>
> >>
> >> p.s.  I'm trying to create an animation by repeatedly calling a function
> >> that contains something like text(0, 1, "abc").  By computing on the
> >> language object 'text(0, 1, "abc")', I can call text(0, 1, 'a') the
> >> first time, text(0, 1, 'ab') the second, and text(0, 1, 'abc') the
> >> third.  The function will be more general if I can get the names of the
> >> arguments as just described.
> >>
> >> ______________________________________________
> >> R-help at r-project.org mailing list
> >> 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.
> 
> 
> --
> Spencer Graves, PE, PhD
> President and Chief Technology Officer
> Structure Inspection and Monitoring, Inc.
> 751 Emerson Ct.
> San José, CA 95126
> ph:  408-655-4567
> web:  www.structuremonitoring.com