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

[Michael Bedward]

Or yet another way which is (I think) a bit closer to your requirement...

f <- function(x) {
  if (missing(x)) cat("x is missing \n")
  else cat("x was provided \n")
}

g <- function(x) {
  if (missing(x))
    fcall <- call("f")
  else
    fcall <- call("f", x)

  eval(fcall)
}


On 13 November 2010 20:24, Michael Bedward <michael.bedward at gmail.com> wrote:
> 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?)
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>