[R] Testing for existence inside a function [Broadcast]

[Talbot Katz]

Hi, Andy.

Thank you for the quick response!  Unfortunately, none of these are exactly 
what I'm looking for.  I'm looking for the following:  Suppose object y 
exists and object z does not exist.  If I pass y as the value of the 
argument to my function, I want to be able to verify, inside my function, 
the existence of y; similarly, if I pass z as the value of the argument, I 
want to be able to see, inside the function, that z doesn't exist.

The missing function just checks whether the argument is missing; in my 
case, the argument is not missing, but the object may not exist.  And the 
way you use the exists function inside the user-defined function doesn't 
test the argument to the user-defined function, it's just hard-coded for the 
object y.  So I'm sorry if I wasn't clear before, and I hope this is clear 
now.  Perhaps what I'm attempting to do is unavailable because it's a bad 
programming paradigm.  But even an explanation if that's the case would be 
appreciated.

--  TMK  --
212-460-5430	home
917-656-5351	cell



>From: "Liaw, Andy" <andy_liaw at merck.com>
>To: "Talbot Katz" <topkatz at msn.com>,r-help at stat.math.ethz.ch
>Subject: RE: [R] Testing for existence inside a function  [Broadcast]
>Date: Tue, 15 May 2007 11:03:12 -0400
>
>Not sure which one you want, but the following should cover it:
>
>R> f <- function(x) c(x=missing(x), y=exists("y"))
>R> f(1)
>     x     y
>FALSE FALSE
>R> f()
>     x     y
>  TRUE FALSE
>R> y <- 1
>R> f()
>    x    y
>TRUE TRUE
>R> f(1)
>     x     y
>FALSE  TRUE
>
>Andy
>
>From: Talbot Katz
> >
> > Hi.
> >
> > I'm having trouble testing for existence of an object inside
> > a function.
> >
> > 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.  Is this
> > possible, or do I have to either check outside the function
> > or pass the name
> > of the argument as a separate argument?
> >
> > If I do exists(x)  or exists(eval(x)) inside the function and
> > y does not
> > exist, it generates an error message.  If I do exists("x") it
> > says that x
> > exists even if y does not.  If I had a separate argument to
> > hold the text
> > string "y" then I could check that.  But is it possible to check the
> > existence of the argument inside the function without passing
> > its name as a
> > separate argument?
> >
> > Thanks!
> >
> > --  TMK  --
> > 212-460-5430	home
> > 917-656-5351	cell
> >
> > ______________________________________________
> > R-help at stat.math.ethz.ch 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.
> >
> >
> >
>
>
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