[R] sys.frame() and variables from parent frame

[David Winsemius]

On Feb 27, 2013, at 1:11 AM, Zé Miguel wrote:

> Dear David,
> 
> thanks for your reply. Sorry for the ambiguous example. I guess the get() will do it, but I still have a question regarding the parent frame. If I declare both function g and f in the global environment:
> 
> g <- function()
> {
> get(N,envir = ???)
> write(N)
> }
> 
> f<-function()
> {
> N<-99
> g()
> }
> 
> What is the environment I should be evoking in the get() function? Excuse me for the bad coding, I jst migrated from another language, please interpret it as a generic language.
> 

You can specify the global environment with either a function call or by a consant name

 globalenv()

 .GlobalEnv


In your code however, 'N' is not in the global environment and you are not passing a character argument to get() as you had been in your first example. Furthermore you have chosen to use write which does not gte the desired effect of reporting from inside a function.

g <- function()
{
get("N", envir = .GlobalEnv)  # character argument to get 
cat(N)
}

f<-function()
{
N<-99  # not in the global environment
g()
}

N <- 42  # assigned in the global environment
f()
# returns 42

-- 
David.



> Cheers,
> 
> José
> 
> 
> 
> 
> On 27 February 2013 01:20, David Winsemius <dwinsemius at comcast.net> wrote:
> 
> On Feb 26, 2013, at 2:40 AM, José Miguel Delgado wrote:
> 
> > Dear R-help,
> >
> > I wrote the following lines in order to use a variable from a parent frame in my callM() function. I would like to solve this by only editing the callM(function). When I run this code I obtain a empty list, meaning that eval(ls(),sys.frame(-1)) could not access the variables in the parent function. Any suggestions? Thanks in advance!
> >
> > metaCall <- function()
> >  {
> >    NN <- 99
> >    callM()
> >    }
> >
> > callM <- function()
> >  {
> >    Ls <- eval(ls(),sys.frame(-1))
> >    print(Ls)
> >    ### use Ls to call a certain model named M
> 
> That doesn't make much sense.
> 
> >    }
> >
> > metaCall()
> >
> 
> I don't think you need the eval() call:
> 
>  metaCall <- function()
>  {
>    NN <- 99
>    callM()
>    }
> 
> callM <- function()
>  {
>    Ls <- ls(env=sys.frame(-1))
>    cat(Ls)
>    }
> 
> metaCall()
> NN
> 
> You should be aware that metaCall will not return anything since the last value is from the cat()-call or the print()-call and they each return NULL. If you wanted to go on from there and do something with 'NN", which is no longer a number but rather a character vector, you could, however.
> 
> Oh, I think I finally see .... the eval() was an attempt to retrieve  the object named "NN"" in the parent.frame? That means you need :
> 
> ?get
> 
> metaCall <- function()
>  {
>    NN <- 99
>    callM()
>    }
> 
> callM <- function()
>  {
>    Ls <- ls(env=sys.frame(-1))
>    str(get(Ls, env=sys.frame(-1)))
>    }
> 
> metaCall()
> # num 99
> 
> --
> David Winsemius
> Alameda, CA, USA
> 
> 
> 
> 
> -- 
> José Miguel Delgado
> Reichenberger Str. 52
> 10999 Berlin
> Tel. 0176 9633 92 56

David Winsemius
Alameda, CA, USA