[R] getting arg names in function calls?

[Hadley Wickham]

You might find it helpful to read
http://adv-r.had.co.nz/Expressions.html, and look at pryr::
standardise_call().

Hadley

On Tue, Apr 8, 2014 at 6:52 PM, Spencer Graves
<spencer.graves at structuremonitoring.com> wrote:
> 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
>
>
> ______________________________________________
> 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.



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