[R] Testing for existence inside a function

[Alberto Monteiro]

Talbot Katz wrote:
> 
> I'm having trouble testing for existence of an object inside a function.
> 
No, you are having trouble testing for existence of an object
_before_ the function is called :-)

> Suppose I have a function:
> 
> f<-function(x){
> ...
> }
> 
> and I call it with argument y:
> 
> f(y)
> 
> I'd like to check inside the function whether argument y exists.
>
This can't be done, because the error happens before f is called.

Try this:

f <- function(x) x + 1
f(y.does.not.exist)
y.does.not.exist

The error message is (almost) the same, and it happens when
parsing the line. There's no way to change f to change this.

Alberto Monteiro