[R] how can I attach a variable stored in

[Peter Waltman]

Hi Mark -

Thanks for the reply.  Sorry I didn't really clarify too well what I'm 
trying to do.  The issue is not that I can't see the variable that gets 
loaded. 

The issue is that the variable is a list variable, and I'd like to write 
a function that will take the .RData filename and attach the variable it 
contains so that I can more easily access its contents, i.e.

    foo.bar <- list( "a"= "a", "b"=1 )
    save( file="foo.bar.RData", foo.bar )
    rm( foo.bar )

    my.fn <- function( fname ) {
       load( fname )
       attach( ls( pat="foo" ) ) #  I want to attach( foo.bar ), but
    this doesn't work
    }

    ls()  # prints out "foo.bar"

    attach( ls( ) )   # still doesn't work
    attach( foo.bar )  # works

So, basically, the question is how can I attach the variable that's 
stored in a file if I don't already know it's name?

Thanks again!

Peter

Leeds, Mark (IED) wrote:
> I don't think I understand your question but John Fox has written a very
> nice documentat about scoping and environments on his website.
> It's probably easy to find the site by googling "John Fox" but, if you
> can't find it, let me know.
>  
> As I said, I don't think that I understand your question but, if you
> loaded a list variable using load("whatever.Rdata"), the variable will 
> just be suitting in  your workspace. You don't need to attach anything
> because load just loads the data right into the workspace.
> So typing the variable name should show the data.
>
>
>
>
> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
> On Behalf Of Peter Waltman
> Sent: Thursday, September 20, 2007 1:32 PM
> To: r-help at r-project.org
> Subject: [R] how can I attach a variable stored in
>
> Hi -
>
> Any help would be greatly appreciated.
>
> I'm loading a list variable that's stored in an .RData file and would
> like attach it.
>
> I've used attach( <file_name> ), but that only lets me see the variable
> that's stored in the file. 
>
> As the variable name is of the form "comp.x.x", I've tried using attach(
> ls( pat="comp" ) ), but get an error as ls() just gives back a string.
>
> I've also played around with eval(), but don't really quite get what
> that function does since it seems to get into the R internals which I
> don't entirely understand and I haven't found any great unified
> documentation on R's handling environment and scoping.
>
> Thanks,
>
> Peter Waltman
>
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