[R] Testing for existence inside a function

[Talbot Katz]

Hi.

Thanks once more for the swift response.  This solution works pretty well.  
The only small glitch is if I pass the function an argument with the same 
name as the function argument.  That is, suppose "x" is the argument name in 
my user-defined function, and that object "x" does not exist.  If I call the 
function f(x), i.e., using the non-existent object x as the argument value, 
then the function says that x exists.

Here is my example log:

>chkex5 <- function(objn){
+ c(exob=exists(deparse(substitute(objn))))
+ }
>exists("objn")
[1] FALSE
>chkex5(objn)
exob
TRUE
>

But I suppose I can live with this.  Thanks again!


--  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
>Date: Tue, 15 May 2007 11:41:17 -0400
>
>Just need a bit more work:
>
>R> f <- function(x) exists(deparse(substitute(x)))
>R> f(y)
>[1] FALSE
>R> y <- 1
>R> f(y)
>[1] TRUE
>R> f(z)
>[1] FALSE
>
>Andy
>
>From: 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.
> > > >
> > > >
> > > >
> > >
> > >
> > >-------------------------------------------------------------
> > -----------------
> > >Notice:  This e-mail message, together with any attachments, contains
> > >information of Merck & Co., Inc. (One Merck Drive,
> > Whitehouse Station,
> > >New Jersey, USA 08889), and/or its affiliates (which may be known
> > >outside the United States as Merck Frosst, Merck Sharp & Dohme or MSD
> > >and in Japan, as Banyu - direct contact information for affiliates is
> > >available at http://www.merck.com/contact/contacts.html) that may be
> > >confidential, proprietary copyrighted and/or legally
> > privileged. It is
> > >intended solely for the use of the individual or entity named on this
> > >message. If you are not the intended recipient, and have
> > received this
> > >message in error, please notify us immediately by reply
> > e-mail and then
> > >delete it from your system.
> > >
> > >-------------------------------------------------------------
> > -----------------
> >
> >
> >
> >
>
>
>------------------------------------------------------------------------------
>Notice:  This e-mail message, together with any attachments...{{dropped}}