R devel - May 2007 - changing the mode of a factor (PR#9675)

Full_Name: Fr?d?ric Gosselin
Version: 2.5 vs 2.4 and 2.2.1
OS: windows XP
Submission from: (NULL) (195.221.118.52)


#############
L3 <- LETTERS[1:3]
 (d <- data.frame(cbind(x=1, y=1:10), fac=as.factor(sample(L3, 10,
repl=TRUE))))
mode(d[,3])<-"numeric"
###############

when trying to change the mode of a column in a data.frame that is a factor to
numeric(cf. preceding code), the following error occurs (in French) in R 2.5:

Erreur dans `storage.mode<-`(`*tmp*`, value = "double") : 
        le mode de stockage d'un objet "factor" ne peut ?tre
modifi?

The same thing works fine in R2.4 and 2.2.1. 

It does not seem to correspond to new things announced in the NEWS file for the
2.5 version...

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How about the following NEWS item (a bug fix)

     o	Assigning class "factor" to an object now requires it has
 	integer (and not say double) codes.

?  (Changing the mode to double amounted to creating a new double vector 
and then assigning the attributes of the old object including the class.
We gave a more specific error message in this case in an attempt to be 
helpful ....)
>From ?factor
      'factor' returns an object of class '"factor"'
which has a set of
      integer codes the length of 'x' with a
'"levels"' attribute of
      mode 'character'.  If 'ordered' is true (or
'ordered' is used) the
      result has class 'c("ordered", "factor")'.

So a factor necessarily has integer codes.  That you were able to change 
the mode in earlier versions of R was a bug that has been fixed.

You may well want one of the answers to FAQ 7.10.


Please take note of the 'BUGS' section in the FAQ and the posting guide:
three incorrect bug items in one day is unhelpful.


On Fri, 11 May 2007, frederic.gosselin at cemagref.fr wrote:
> Full_Name: Fr?d?ric Gosselin
> Version: 2.5 vs 2.4 and 2.2.1
> OS: windows XP
> Submission from: (NULL) (195.221.118.52)
>
>
> #############
> L3 <- LETTERS[1:3]
> (d <- data.frame(cbind(x=1, y=1:10), fac=as.factor(sample(L3, 10,
> repl=TRUE))))
> mode(d[,3])<-"numeric"
> ###############
>
> when trying to change the mode of a column in a data.frame that is a factor
to
> numeric(cf. preceding code), the following error occurs (in French) in R
2.5:
>
> Erreur dans `storage.mode<-`(`*tmp*`, value = "double") :
>        le mode de stockage d'un objet "factor" ne peut ?tre
modifi?
>
> The same thing works fine in R2.4 and 2.2.1.
>
> It does not seem to correspond to new things announced in the NEWS file for
the
> 2.5 version...
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595
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