problem with repeated formal arguments and ...
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 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