[R] problems with assigning a class to an environment

[Peter Dalgaard BSA]

Jens Oehlschlägel <joehl at gmx.de> writes:

> I was surprised to find that calling str() on an environment can remove
> attributes from it, as in
> 
> > a <- new.env()
> > class(a) <- "jens"
> > class(a)
> [1] "jens"
> > str(a)
> Class 'jens' length 0 <environment>
> > class(a)
> NULL
> 
> then I found in the R-Language-Manual in chapter 2.1.10 Environments the
> sentence: 
> 
> 	"In particular, assigning attributes to an environment can lead to
> surprises"
> 
> Can please someone familiar with the internals explain what's going on?

The main issue is that environments aren't copied on assignment, so
stuff like y <- unclass(x) will remove the class attribute from x if x
is an environment. Or, as is the case here, str(unclass(x)) will do it.


> Is it save, to assign a class to a list which contains an environment?

Yes, and the recommended way.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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