Question

Is it possible to have multiple ellipsis arguments in an R function? A simplified version of what I’m trying to do is this:

plotgenerator<-function(x,y,...,...,...){
   plot(x,y,...)
   axes(...)
   legend(...)
   }

My thought was to use optional string arguments, like this:

plotgenerator<-function(x,y,plotargs="",axesargs="",legendargs=""){
   plot(x,y,plotargs)
   axes(axesargs)
   legend(legendargs)
   }

But that doesn’t work. Does anyone know if something like this is possible? I have searched a lot for this, but a search string like “R …” isn’t actually very helpful 😉

Answer 1

You could so something similar to your second choice if you use do.call, which allows you to pass the arguments to a function as a list. E.g. pass axesarg as a list and then in your function have: do.call(axes,axesarg) etc

For example:

outer_fxn <- function(inner_args=list(), ...) {
    do.call(inner_fxn, inner_args)
}

inner_fxn <- function(...) {
    # do stuff
}

# function call
outer_fxn(inner_args=list(a=1, b=2), outer_arg1=3, etc)

In the above, any arguments that should be handled by the inner_fxn ... should be passed in with in the inner_args list. The outer_fxn ... arguments are handled as usual.