modify "..." (optional args)

Fri, Oct 7, 2011 1:39 AM #

Hi all,

Is there a way to modify the optional arguments (...) passed to a 
function, so that these can be passed in modified form to a subsequent 
function call? I checked "Programming with Data" but could not find a 
solution there.

What I'd like is something along these lines:

test <- function(x,y,...) {
   if(!hasArg(xlab)) { ___add xlab to ...___ }
   if(hasArg(xlab)) { ___remove xlab from ...___ }  # alternative

   plot(x,y,...)
}

Of course, I could use separate calls, like

if(hasArg(xlab)) plot(x,y,...) else plot(x,y,xlab="label",...)

but this gets complicated if there is more than one such case to consider.

Thanks

Pascal

Pascal A. Niklaus
Institute of Evolutionary Biology and Environmental Studies
University of Zurich
Winterthurerstrasse 190
CH-8057 Zurich / Switzerland

Duncan Murdoch

Fri, Oct 7, 2011 5:13 AM #

On 11-10-07 4:39 AM, Pascal A. Niklaus wrote:

Not as such, but you get the same result using do.call.  For example:

test <- function(x, y, ...) {
   args <- list(x=x, y=y, ...)
   if (!hasArg(xlab)) args <- c(args, list(xlab="My label"))
   do.call(plot, args)
}

This has a disadvantage that the argument to plot has already been 
evaluated, so the y label shows the value rather than the expression 
test() received for y.  Presumably you can construct a call and evaluate 
it to get the labels you want; the tools are quote(), bquote(), 
substitute(), etc.

Duncan Murdoch