[R] Testing for existence of object within a function
Phil Spector
spector at stat.berkeley.edu
Fri Oct 8 01:39:41 CEST 2010
Eli -
I think you're looking for missing():
> tst = function(a,b=1)
+ if(missing(a))print("You must provide a") else print(a)
> tst()
[1] "You must provide a"
> tst(7)
[1] 7
- Phil Spector
Statistical Computing Facility
Department of Statistics
UC Berkeley
spector at stat.berkeley.edu
On Thu, 7 Oct 2010, Eli Holmes wrote:
> I'm trying to test for the existence of an object within a function,
> but despite searching the help files and R-list, I can't figure out
> how to do it.
>
> Here is some test code:
>
> #-------------------------
> a=1 #now I have a in the global environment
>
> tst <- function(a,b=1) {
> # but a is not in the local function environment
> print(exists("a", inherits=FALSE)) #This is how I think I should be
> able to test if it is in the local function environment
> print(a)
> }
> tst()
> #----------------------
>
> #Here's the output
> [1] TRUE
> Error in print(a) : argument "a" is missing, with no default
>
> It says TRUE, even though I specified inherits=FALSE and "a" is not in
> the function environment. I've tried to pass in where and envir
> arguments to exists() but I haven't been able to solve the problem.
>
> Thanks in advance.
>
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