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_schwartz@me.com> wrote:

From: Marc Schwartz <marc_schwartz@me.com>
Subject: Re: [R] how to determine if a variable is already set?
To: "carol white" <wht_crl@yahoo.com>
Cc: r-help@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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