Handling argument priorities (specified vs argument list vs default) in R

argument-handling.R

# Sometimes during repeat calls to a function, it may be helpful if arguments used in a 
# previous call are passed as a list to the function in subsequent calls, to be 
# superseded if individual arguments of the same name are given.
#
# The following function prioritises specified arguments (including ... arguments) over an
# argument list, and the argument list over default values.

handle_args <- function(arg1 = 1, arg2 = 2, arglist = list(), ...) {
  
  # Copy default arguments
  dargs <- as.list(sys.frame(sys.nframe()))
  dargs <- lapply(dargs, eval, parent.frame())

  # Copy specified arguments
  cargs <- as.list(match.call())[-1L]
  cargs <- lapply(cargs, eval, parent.frame())

  # Remove arglist from the default and specified arguments
  dargs[["arglist"]] <- NULL
  cargs[["arglist"]] <- NULL

  # Compile arguments into a single list:
  
  # - privilege the arglist elements over the defaults
  all_args <- append(arglist, dargs[!(names(dargs) %in% names(arglist))])
  
  # - privilege specified arguments over the rest
  all_args <- append(cargs, all_args[!(names(all_args) %in% names(cargs))])
  
  return(all_args)
  
}

## Examples
#
# handle_args(arglist = list(arg1 = 3))
# handle_args(arglist = list(arg1 = 3, arg3 = 0))
# handle_args(arg1 = 4, arglist = list(arg1 = 3, arg3 = 0))
# handle_args(arg1 = 4, arglist = list(arg1 = 3, arg3 = 0), arg3 = 1)
# handle_args(arg1 = 4, arglist = list(arg1 = 3, arg2 = 4, arg3 = 0), arg3 = 1)