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Scoping question

2 messages · iuhz7j202 at sneakemail.com, Simon Urbanek

Original
iuhz7j202 at sneakemail.com
# 
Hi,

I'm struggling with a bit of scoping using the with() function. I think it's best explained with an example:
  x <- list(foobar=2)
  f <- function(){foobar*2}
  with(x,f())
This throws an error that 'foobar' does not exist. However if I define foobar in the global environment, f will find it whether I call it from the global environment or from within x. I have also tried using get("foobar",parent.frame()) within f, along with other variations, with no success.

I could always just add foobar as an argument to f, but in my actual work case foobar is a potentially very large object that is not worth making a copy of. (I don't know how much of an effect this will actually have on performance). I also just don't like all the bookkeeping of having to know which objects in x I am going to need in f and passing them all as arguments.

I would appreciate any insight about why the scoping is not working as I thought it would, and if there is any way to get around it without directly passing arguments to f.

Thank you,
Peter
Simon Urbanek
# 
Peter,

this is a list for Mac-related issues. Please use R-help for general  
questions for help - or actually just read about the difference  
between lexical and dynamic scoping (R uses the former which means  
that f will be evaluated in the global environment so there will be no  
foobar).

Cheers,
Simon
On Apr 14, 2009, at 12:08 , iuhz7j202 at sneakemail.com wrote: