[R] How to set an argument such that a function treats it as missing?

[Michael Bedward]

Hello Marius,

NULL is not the same as missing. You could something like this in
various ways. Here are a couple...

g <- function(x) {
  if (missing(x)) {
    f()
  } else {
    f(x)
  }
}

or change f to detect null args

g <- function(x) {
  if (missing(x)) {
    x <- NULL
  }

  f(x)
}

f <- function(x) {
  if (missing(x) | is.null(x)) {
    // do something
  }
}


Michael


On 13 November 2010 19:14, Marius Hofert <m_hofert at web.de> wrote:
> Dear expeRts,
>
> I would like to call a function f from a function g with or without an argument.
> I use missing() to check if the argument is given. If it is not given, can I set
> it to anything such that the following function call (to f) behaves as if the argument
> isn't given? It's probably best described by a minimal example (see below).
>
> The reason why I want to do this is, that I do not have to distinguish between the
> cases when the argument is given or not. By setting it to something (what?) in the
> latter case, I can use the same code in the subsequent part of the function.
>
> Cheers,
>
> Marius
>
>
>
> f <- function(x) if(missing(x)) print("f: missing x") else print(x)
>
> g <- function(x){
>        if(missing(x)){
>                print("g: missing x")
>                x <- NULL # I try to set it to something here such that...
>        }
>        f(x) # ... this call to f behaves like f()
> }
>
> g() # should print "f: missing x" (is this possible?)
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