Message-ID: <4304E5B4.60709@pdf.com>
Date: 2005-08-18T19:47:00Z
From: Sundar Dorai-Raj
Subject: problem with repeated formal arguments and ...
In-Reply-To: <4304D751.2080400@pdf.com>
Sundar Dorai-Raj wrote:
>
> Ross Boylan wrote:
>
>>I want to add an argument if it is not present. Following the Green
>>Book, p. 337:
>>test <- function(x, ...){
>> dots <- list(...)
>> if (!hasArg(from))
>> from <- 0
>> else
>> from <- dots$from
>> curve(x, from=from, ...)
>>}
>>
>>
>>
>>>test(sin)
>>>test(sin, from=4)
>>
>>Error in curve(x, from = from, ...) : formal argument "from" matched by
>>multiple actual arguments
>>
>>The FAQ says, in the section on differences between R and S,
>>"R disallows repeated formal arguments in function calls."
>>
>>That seems a perfectly reasonable rule, but how do I handle this
>>situation?
>>
>
>
> Hi, Ross,
>
> Add "from" to your function:
>
> test <- function(x, from = 0, ...) {
> curve(x, from = from, ...)
> }
>
> Or another way:
>
> test <- function(x, ...) {
> dots <- list(...)
> if(!hasArg(from)) dots$from <- 0
> dots$expr <- x
> do.call("curve", dots)
> }
>
I didn't check this example, but for curve, since `x' is an expression,
we should actually do the following:
test <- function(x, ...) {
dots <- list(...)
if(!hasArg(from)) dots$from <- 0
dots$expr <- substitute(x)
invisible(do.call("curve", dots))
}
test(x^3 - 3 * x, to = 5)
test(x^3 - 3 * x, from = -5, to = 5)
HTH,
--sundar
> I actually prefer the latter if I'm changing many arguments. I do this
> quite often when writing custom lattice plots and I want to override
> many of the defaults.
>
> HTH,
>
> --sundar
>
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