[R] attach

Peter Dalgaard p.dalgaard at biostat.ku.dk
Sat Oct 17 10:11:43 CEST 2009


Dieter Menne wrote:
> 
> 
> Christophe Dutang1 wrote:
>>
>> I would like to know what happens on the memory side when I use
>> attach(inputdata)
>>
>> Is there a second allocation of memory for inputdata?
>>
> 
> Not, it just guides the syntax.

Wrong. There's a virtual copy of data plus a conversion from data frame 
to attached environment on the search path. If you modify data in either 
of the original frame or the environment, you will get duplication.

> 
> Christophe Dutang1 wrote:
>> Is it better not to use attach function?
>>
> 
> A qualified "yes" in the sense of  "do not use it". I think it is used to
> much in old documentation, presumably because some S eggshells.
> 
> I use with() if I have a nasty formula to unclutter; it acts locally only
> and you don't get unwanted side effects.

Well, opinions vary. Having to qualify data frame access on each use 
does tend to get in the way of explorative work, at least it does so for 
me.

-- 
    O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
  (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907



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