[R] Testing for existence inside a function
murdoch at stats.uwo.ca
Tue May 15 21:51:01 CEST 2007
On 5/15/2007 3:06 PM, Alberto Monteiro wrote:
> 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:
>> and I call it with argument 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
> The error message is (almost) the same, and it happens when
> parsing the line. There's no way to change f to change this.
That description is true in some languages, but not in R. R doesn't
check that args to functions are valid until it needs to use them. For
> f <- function(y) 1 # doesn't care if y exists
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