Do watch out, however, for *where* i exits.
That is, if you type search() you will see a list of environments in
which i might be found. You're probably assuming that i, if
exists("i") is true, is in .GlobalEnv, but it might be in one of the
other environments, in which case exists('i') will be TRUE, but it
won't be the i you are looking for.
I believe you need to quote then name also
use: exits('i')
not: exists(i)
See ?exists (again)
-Don
At 10:19 AM -0700 9/12/09, carol white wrote:
Thanks for your replies.
I use the following script:
if(!exists(i)) stop ("set the variable i", call. = FALSE)
but before the stop expression, Error gets displayed:
Error: set the variable i
Is there another function that stops the execution, prints an
expression without printing Error or any other expression except the
expression parameter?
Best,
--- On Fri, 9/11/09, Marc Schwartz <marc_schwa...@me.com> wrote:
From: Marc Schwartz <marc_schwa...@me.com>
Subject: Re: [R] how to determine if a variable is already set?
To: "carol white" <wht_...@yahoo.com>
Cc: r-h...@stat.math.ethz.ch
Date: Friday, September 11, 2009, 10:21 AM
On Sep 11, 2009, at 12:15 PM, carol white wrote:
Hi,
It might be a primitive question but how it is possible to
determine if a variable is initialized in an environment? Suppose
that we start a R session and wants to run a script which use the
variable i. Which function could evaluate if i is already
initialized or not and if not, then ask interactively the user to
set it? This is to avoid the error message: object i is not found.
Regards,
Carol
See ?exists
Note that this will tell you if the object exists, not if it
contains a specifically desired initial value. You would have to
check for the latter after determining that the object does indeed
exist.
HTH,
Marc Schwartz
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--
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062
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