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Messing with the "..." argument

4 messages · Duncan Murdoch, Steve Lianoglou, Wacek Kusnierczyk

Steve Lianoglou
# 
Hi all,

Sorry if this is documented somewhere, but trying to search and google for 
ways to alter my "..." argument is having me chasing my tail.

Is there someway that I can manipulate the elements in "..."? 
Specifically I'd like to use certain vars in "...", then remove them 
from "..." and pass the rest of "..." to another function.

Here's a short example: I'm adding more functionality to a generic 
method by defining how it works on a new class "MyClass":

setMethod('existingFunction', 'MyClass', function (object, ...) {
  vars <- list(...)
  doSomethingWith(vars$myCustomVar)
  
  # now I want to pass the rest of the vars down to another function,
  # let's say some plotting function, so I'd like to remove
  # `myCustomVar` from "...", keep the rest of the vars and just
  # pass the valid "..." elements down through the call chain
  
  doSomePlot(somethingSane, ...)
})

Currently the `doSomePlot` that's called does fine until it passes the
rest of it's vars to the "real" plot method, at which point I'll get
a warning like:

Warning messages:
1: In plot.window(...) : "myCustomVar" is not a graphical parameter
2: In plot.xy(xy, type, ...) : "myCustomVar" is not a graphical parameter
3: In axis(side = side, at = at, labels = labels, ...) :
  "myCustomVar" is not a graphical parameter
4: In axis(side = side, at = at, labels = labels, ...) :
  "myCustomVar" is not a graphical parameter
5: In box(...) : "myCustomVar" is not a graphical parameter
6: In title(...) : "myCustomVar" is not a graphical parameter

Depending on what the name of myCustomVar is, this can work even with
the warnings, which is passable. It might also bail if myCustomVar
happens to share a name with a real plotting var, but has an illegal
value for it.

Anyway, while there are ways it can work in this case, I'm just wondering
if I can remove elements from "..." and side-step these warning/error issues
altogether.

Since "vars <- list(...)" works to create a list of arguments from "...",
I'm guessing there must be a way to take an already existing list variable
and turn its name/value pairs into an appropriate "..." object?

Thanks for any help,
-steve
Duncan Murdoch
#
On 2/12/2009 2:34 PM, Steve Lianoglou wrote:
I don't think so, but an alternative is to put together a parameter list 
and call do.call().  For example,

 > g <- function(...) {
+    list(...)    # just return the arg list to see what arrived
+ }
 >
 > f <- function(...) {
+    all <- list(...)
+    all["nothanks"] <- NULL
+    do.call("g", all)
+ }
 >
 > g(nothanks=1, yesplease=2)
$nothanks
[1] 1

$yesplease
[1] 2

 > f(nothanks=1, yesplease=2)
$yesplease
[1] 2

Duncan Murdoch
Steve Lianoglou
# 
Hi Duncan,
Nice!

Yeah, that did the trick quite well ... 

Thanks,
-steve
Wacek Kusnierczyk
# 
here's an example which may give you a hint -- it is not supposed to
solve your particular problem:

f = function(...)
    list(...)
g = function(...) {
    args = list(...)
    names = names(args)
    if (is.null(names))
       f(...)
    else
        do.call(f, args[names(args) != 'foo']) }

g()
# list()
g(1)
# list(1)
g(a=1)
# list(a=1)
g(a=1, foo=2)
# list(a=1)
g(1, foo=2)
# list(1)
g(foo=1)
# list()

consider using grep for finding the variables to be removed.

vQ
Steve Lianoglou wrote: