[R] how can I attach a variable stored in

[Tony Plate]

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: 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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