Re: [R] getting arg names in function calls?

Spencer Graves Wed, 09 Apr 2014 14:31:30 -0700

      Thanks very much to both Bill Dunlap and Hadley Wickham.

Per Bill's second suggestion, "match.call(eval(bo[[1]]), bo)"returned the desired "plot(x = 0, y = 1)" [with bo <-body(function()plot(0, 1)].

Hadley's "standardise_call(bo)" [from library(pryr)] is muchsimpler.



      Thanks again,
      Spencer


On 4/8/2014 7:49 PM, William Dunlap wrote:

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.gra...@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-boun...@r-project.org [mailto:r-help-boun...@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.

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Re: [R] getting arg names in function calls?

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