levels() counter-intuitif? (PR#1693)
Wed, 19 Jun 2002 18:18:18 +0100 (BST)
On Wed, 19 Jun 2002 firstname.lastname@example.org wrote:
> Suppose I have a factor size with levels "small", "medium" and "large".
> Then, when I subset this factor:
> to get at the extremes,
> Levels: large medium small
> The same happens with
> >subset( size, size!="medium")
> I understand that the resulting factor inherits the possible levels from its
> "parent", but I do not see in what that is useful.
When you have enough experience you may. Lots of R code relies on it, for
a start. It's also essential when predicting a classifcation to know wha
the possible values were. That's the whole point of a factor: it's an
enumeration type, and one does not change the enumeration on subsetting.
> Intuitively, I would
> expect that levels(ss) return "small" and "large". For subset(), there might
> be an option to request inheritance of the number of levels.
There is such an option: [, drop=TRUE].
Please DO NOT use R-bugs to document your intuition.
Brian D. Ripley, email@example.com
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 272860 (secr)
Oxford OX1 3TG, UK Fax: +44 1865 272595
r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !) To: firstname.lastname@example.org