R help - Nov 2010 - How to set an argument such that a function treats it as missing?

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?)

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.
>

On Sat, Nov 13, 2010 at 3:14 AM, 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.
>
You can pass missing values:

f <- function(x) g(x)
g <- function(x) missing(x)
f(3) # FALSE
f() # TRUE


-- 
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com

Marius Hofert 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...
Just leave out the line above, and you'll get both messages printed:

 > g()
[1] "g: missing x"
[1] "f: missing x"

Duncan Murdoch
> 	}
> 	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.