[R] Testing for existence inside a function
Gabor Grothendieck
ggrothendieck at gmail.com
Tue May 15 19:43:21 CEST 2007
Right. Thanks. It should have been parent.frame(). Here is the correction:
chk3 <- function(x) {
chr <- deparse(substitute(x))
e <- parse(text = chr)
structure(exists(chr, parent.frame()),
is.name = length(e) == 1 && is.name(e[[1]]))
}
chk3(1) # structure(FALSE, is.name = FALSE)
ab <- 1
chk3(ab+1) # structure(FALSE, is.name = FALSE)
chk3(ab) # structure(TRUE, is.name = TRUE)
exists("x") # FALSE
chk3(x) # structure(FALSE, is.name = TRUE)
chk3(x+1) # structure(FALSE, is.name = FALSE)
On 5/15/07, Bert Gunter <gunter.berton at gene.com> wrote:
> I think parent.frame() is what is wanted, not parent.env(environment()) in
> your suggested solution:
>
> Consider this: (which does **not** however handle the arbitrary expressions
> as argument issue):
>
>
> foo1 <- function(z){
> cat(exists(deparse(substitute(z)),parent.frame()),
> exists(deparse(substitute(z)),parent.env(environment())),
> exists(deparse(substitute(z))),"\n")
> invisible()
> }
>
> foo <- function(x){
> y <- x
> foo1(y)
> }
>
> x<-1
>
> ## Then ...
> > foo(x)
> TRUE FALSE FALSE
>
> Note that parent.env() is the **enclosing environment** i.e. the environment
> in which foo1 is defined (lexical scoping); while parent.frame() is the
> frame of the caller of foo1, which is what is wanted if foo1 is to work when
> called within a function. Note that parent.frame() would also work when foo1
> is called at the command line.
>
> Further corrections/clarifications welcome, of course.
>
> Bert Gunter
> Genentech Nonclinical Statistics
>
>
>
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Gabor Grothendieck
> Sent: Tuesday, May 15, 2007 10:06 AM
> To: Liaw, Andy
> Cc: r-help at stat.math.ethz.ch; Talbot Katz
> Subject: Re: [R] Testing for existence inside a function
>
> Maybe this:
>
>
> chk2 <- function(x) {
> chr <- deparse(substitute(x))
> e <- parse(text = chr)
> structure(exists(chr, parent.env(environment())),
> is.name = length(e) == 1 && is.name(e[[1]]))
> }
> chk2(1) # structure(FALSE, is.name = FALSE)
> ab <- 1
> chk2(ab+1) # structure(FALSE, is.name = FALSE)
> chk2(ab) # structure(TRUE, is.name = TRUE)
> exists("x") # FALSE
> chk2(x) # structure(FALSE, is.name = TRUE)
> chk2(x+1) # structure(FALSE, is.name = FALSE)
>
>
> On 5/15/07, Liaw, Andy <andy_liaw at merck.com> wrote:
> > Another thing to watch out for is that an argument to a function can be
> > an expression (or even literal constants), instead of just the name of
> > an object. exists() wouldn't really do the right thing. I'm not sure
> > how to properly do the exhaustive check.
> >
> > Andy
> >
> > From: Gabor Grothendieck
> > >
> > > Try this modification:
> > >
> > > > chk <- function(x) exists(deparse(substitute(x)),
> > > parent.env(environment()))
> > > > ab <- 1
> > > > chk(ab)
> > > [1] TRUE
> > > > exists("x")
> > > [1] FALSE
> > > > chk(x)
> > > [1] FALSE
> > >
> > >
> > >
> > > On 5/15/07, Talbot Katz <topkatz at msn.com> wrote:
> > > > 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
> > > > > > > >
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