Change default arguments of an R function at runtime

Question

Is it possible to change the default values of formal parameters in an R function at runtime?

Let\'s assume, we have the function

f <- function(x=1) {         


        

Answer 1

UPDATE: 2020-12-13

This method is no longer available

Yes, the Defaults package allows you to do this.

Answer 2

An alternative (shown in a different SO post) is to use the formals function, e.g.:

formals(f) <- 2

Answer 3

As the Defaults package is no longer available from CRAN, you can use default.

As an example:

x <- list(a = 1, b = 2, c = 3)
default::default(unlist) <- list(use.names = FALSE)
unlist(x)
#> [1] 1 2 3

unlist <- default::reset_default(unlist)
unlist(x)
#> a b c 
#> 1 2 3

Created on 2019-03-22 by the reprex package (v0.2.0.9000).

Answer 4

I tried to do the same argument wrapping for the packagefinder library which has an alias of fp() pointing to findPackage(). I tried all sorts of methods, including using formals(), but in the end, the only thing that worked for me were the following 3 variations:

#--------------------------------------
# packagefinder
#--------------------------------------
# fp = findPackage
# Set default to use: 
#   fp(... , display = "console", return.df = TRUE)
#--------------------------------------
fp <- function(...) {
  packagefinder::fp(..., display="console", return.df=TRUE)
}

fp <- function(...) invisible(findPackage(..., display="console", return.df=TRUE))
fp <- function(..., display="console", return.df=TRUE) packagefinder::fp(...,display=display, return.df=return.df)

The formals() method I could not get to work.

# Fail-1
formals(fp) <- alist(... = , display="console", return.df=TRUE)

# Fail-2
MY_ARGS <- list(display="console", return.df=TRUE)
formals(fp)[names(MY_ARGS)] <- MY_ARGS

---

Other related posts on this:

• R: Passing function arguments to override defaults of inner functions
• Setting Function Defaults R on a Project Specific Basis
• Change a function's default argument for all calls within a scope
• https://www.rdocumentation.org/packages/base/versions/3.6.2/topics/formals