Re: [R] Existence of formal arguments.

From: Erik Iverson <iverson_at_biostat.wisc.edu>
Date: Thu, 05 Jun 2008 19:57:53 -0500

Note the difference between

test <- function(a) {

   exists("a", mode = "symbol")
}
test()

and

test2 <- function(a) {

   exists("a", mode = "numeric") #say
}

test2()

and then note that the default mode argument to exists is "any".

Rolf Turner wrote:
>
> I just discovered what seems to me to be a slight funny in respect
> of formal argument names. If I define a function
>
> foo <- function(a,b){ ... whatever ...}
>
> then ``inside'' foo() the exists() function will return TRUE
> from ``exists("a") whether an object named ``a'' exists or not.
> But get("a") will yield an error ``object "a" not found''
> in these circumstances.
>
> I presume there is a reason for specifying that an object named
> by a formal argument always exists --- but it is mysterious by my
> standards. Can anyone explain the reason for this behaviour?
>
> This is just idle curiosity --- or my hunger for knowledge, whichever
> way you want to look at it :-) --- it doesn't really matter.
>
> cheers,
>
> Rolf Turner
>
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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. Received on Fri 06 Jun 2008 - 01:36:32 GMT

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