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

[Marc Schwartz]

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