[R] how to determine if a variable is already set?

[Bert Gunter]

I don't believe the solution proposed below works and anyway misses the
whole point of tryCatch(), which is **not** to test manually:

f <- function(i){
 val <- tryCatch(get("i"), error = function(e)"input error")
 val ## can test val and carry on if not an error
}

## testit

> f()
[1] "input error"
> f(2)
[1] 2
>

Bert Gunter
Genentech Nonclinical Biostatistics

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of Henrique Dallazuanna
Sent: Monday, September 14, 2009 12:44 PM
To: carol white
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] how to determine if a variable is already set?

Try this:

if (!exists("i"))
   tryCatch(stop(""),
          error = function(e)invisible(),
            finally=print("Please set the i variable"))

On Mon, Sep 14, 2009 at 3:38 PM, carol white <wht_crl at yahoo.com> wrote:

> Thanks to your replies.
>
> In fact, the problem doesn't come from "exists" but from "stop" that
> displays Error even if call. = FALSE. To answer to Dan, I quoted the
> pramater of exists. So when the variable is not defined, stop displays the
> expression message preceded by "Error". So the question was how not to
> display "Error" or if there is another function that does stop's job
without
> displaying "Error"?
>
> Cheers,
>
> --- On Sun, 9/13/09, Michael Knudsen <micknudsen at gmail.com> wrote:
>
> From: Michael Knudsen <micknudsen at gmail.com>
> Subject: Re: [R] how to determine if a variable is already set?
> To: "carol white" <wht_crl at yahoo.com>
> Cc: r-help at stat.math.ethz.ch
> Date: Sunday, September 13, 2009, 7:06 AM
>
> On Fri, Sep 11, 2009 at 7:15 PM, carol white <wht_crl at yahoo.com> wrote:
>
> > It might be a primitive question but how it is possible to determine if
a
> variable is initialized in an environment?
>
> What about this?
>
> > "x" %in% ls()
> [1] FALSE
> > x = 41
> > "x" %in% ls()
> [1] TRUE
>
> Best,
> Michael
>
> --
> Michael Knudsen
> micknudsen at gmail.com
> http://lifeofknudsen.blogspot.com/
>
>
>
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org 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.
>



-- 
Henrique Dallazuanna
Curitiba-Parana-Brasil
250 25' 40" S 490 16' 22" O

	[[alternative HTML version deleted]]