Here's a function that does what I think you want to do:
> attach.firstvar <- function(file) {
+ tmpenv <- new.env()
+ vars <- load(file, envir=tmpenv)
+ x <- get(vars[1], envir=tmpenv, inherits=FALSE)
+ if (is.list(x))
+ attach(x, name=vars[1])
+ return(vars)
+ }
> x <- list(xa=1, xb=2, xc=3)
> save(list="x", file="tmp1.rda")
> remove(list="x")
> attach.firstvar("tmp1.rda")
[1] "x"
> ls(pos=2)
[1] "xa" "xb" "xc"
> find("xa")
[1] "x"
> search()
[1] ".GlobalEnv" "x" "package:stats"
[4] "package:graphics" "package:grDevices" "package:utils"
[7] "package:datasets" "package:methods" "Autoloads"
[10] "package:base"
> xa
[1] 1
> xb
[1] 2
>
Peter Waltman wrote:
> 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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
>> On Behalf Of Peter Waltman
>> Sent: Thursday, September 20, 2007 1:32 PM
>> To: r-help@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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