R devel - Sep 2004 - attaching to position 1

If an attempt is made to attach to position 1, it appears to work
(not even a warning) but in fact it doesn't work as many would
expect.  "search" thinks that it gets placed in position 2, but
nothing
is actually there (according to "ls").

This is guaranteed to be confusing (and annoying) to people who
are used to attaching to position 1 in S-PLUS.

I'm not clear on all of the implications of changing this, but my
first inclination would be to make it an error to attach to position 1.
The help file says that you can't do it.

At the very least there should be a warning .  My guess is that it is
rare for someone to attach to position 1 and not attempt to modify
what is being attached.

 > attach('foo.RData')
 > search()
 [1] ".GlobalEnv"        "file:foo.RData"   
"package:methods"
 [4] "package:stats"     "package:graphics" 
"package:grDevices"
 [7] "package:utils"     "package:datasets" 
"Autoloads"
[10] "package:base"    
 > ls(2)
[1] "jj"
 > jj
[1] 1 2 3 4 5 6 7 8 9
 > detach()
 > search()
[1] ".GlobalEnv"        "package:methods"  
"package:stats"
[4] "package:graphics"  "package:grDevices"
"package:utils"
[7] "package:datasets"  "Autoloads"        
"package:base"
 > attach('foo.RData', pos=1)
 > search()
 [1] ".GlobalEnv"        "file:foo.RData"   
"package:methods"
 [4] "package:stats"     "package:graphics" 
"package:grDevices"
 [7] "package:utils"     "package:datasets" 
"Autoloads"
[10] "package:base"    
 > ls(2)
character(0)

         _                          
platform i386-pc-mingw32            
arch     i386                       
os       mingw32                    
system   i386, mingw32              
status   Under development (unstable)
major    2                          
minor    0.0                        
year     2004                       
month    09                         
day      17                         
language R 


Pat

>>>>> "PatBurns" == Patrick Burns
<pburns@pburns.seanet.com>
>>>>>     on Wed, 22 Sep 2004 18:30:10 +0100 writes:
    PatBurns> If an attempt is made to attach to position 1, it
    PatBurns> appears to work (not even a warning) but in fact
    PatBurns> it doesn't work as many would expect.  "search"
    PatBurns> thinks that it gets placed in position 2, but
    PatBurns> nothing is actually there (according to "ls").

    PatBurns> This is guaranteed to be confusing (and annoying)
    PatBurns> to people who are used to attaching to position 1
    PatBurns> in S-PLUS.

yes; thanks for bringing this up!

    PatBurns> I'm not clear on all of the implications of
    PatBurns> changing this, but my first inclination would be
    PatBurns> to make it an error to attach to position 1.  The
    PatBurns> help file says that you can't do it.

and has done so for a long time AFAIR.

    PatBurns> At the very least there should be a warning .  My
    PatBurns> guess is that it is rare for someone to attach to
    PatBurns> position 1 and not attempt to modify what is being
    PatBurns> attached.

Hence (together with the arguments further above),
I think an error would be more appropriate
[if there's only a warning and the user's code continues on 
 the wrong assumption, more problems lay ahead].

OTOH, in the current "beta" phase I can think of a case where an
error would be too "hard": 
The worst I can see is an R script that has attach(*, pos=1)
which doesn't attach at all {as you say, it *seems* to attach to
position 2 but doesn't really provide the object}, but for some
reason still continues to produce reasonable things.

Hene, for 2.0.0 in "deep freeze", I'd propose to give a warning
only.
However, we wouldn't the database' to search()[2]  "seemingly"
only,
and this could be a problem if a user's script does a detach(..) later.
I.e., we should attach() to pos=2 *properly* (instead of
"seemingly") only.

At the latest for 2.1.0, we should rather make the warning an error.

In any case, this looks like a very simple fix (to the C
source);

Martin Maechler





    >> attach('foo.RData')
    >> search()
    PatBurns> [1] ".GlobalEnv"        "file:foo.RData"   
"package:methods"
    PatBurns> [4] "package:stats"     "package:graphics" 
"package:grDevices"
    PatBurns> [7] "package:utils"     "package:datasets" 
"Autoloads"
    PatBurns> [10] "package:base"    
    >> ls(2)
    PatBurns> [1] "jj"
    >> jj
    PatBurns> [1] 1 2 3 4 5 6 7 8 9
    >> detach()
    >> search()
    PatBurns> [1] ".GlobalEnv"        "package:methods"  
"package:stats"
    PatBurns> [4] "package:graphics"  "package:grDevices"
"package:utils"
    PatBurns> [7] "package:datasets"  "Autoloads"        
"package:base"
    >> attach('foo.RData', pos=1)
    >> search()
    PatBurns> [1] ".GlobalEnv"        "file:foo.RData"   
"package:methods"
    PatBurns> [4] "package:stats"     "package:graphics" 
"package:grDevices"
    PatBurns> [7] "package:utils"     "package:datasets" 
"Autoloads"
    PatBurns> [10] "package:base"    
    >> ls(2)
    PatBurns> character(0)

    PatBurns> _                          
    PatBurns> platform i386-pc-mingw32            
    PatBurns> arch     i386                       
    PatBurns> os       mingw32                    
    PatBurns> system   i386, mingw32              
    PatBurns> status   Under development (unstable)
    PatBurns> major    2                          
    PatBurns> minor    0.0                        
    PatBurns> year     2004                       
    PatBurns> month    09                         
    PatBurns> day      17                         
    PatBurns> language R