From: ripley@stats.ox.ac.uk
Date: Thu 09 Jan 2003 - 04:23:03 EST
Message-id: <Pine.LNX.4.31.0301081717210.16534-100000@gannet.stats>
Well, the xtable package is at fault. One really should not assume an
object has no class, and should only check inheritance.
That function should have
if(is.null(class(x))) class(x) <- data.class(x)
switch(class(x), ....)
On Wed, 8 Jan 2003, Nunoo, Paa K wrote:
> Hi,
>
> Loading the "methods" package into R seems to change the class of a
> character vector from NULL to "character":
>
> > class("abcd")
> NULL
> > library("methods")
> > class("abcd")
> [1] "character"
>
> This can lead to problems. For example the "as.string" function in the
> "xtable" package
> assumes that the class of a character vector is NULL. However this changes
> when the methods
> package is loaded.
>
> Here is a code snippet of the as.string function in the xtable package:
> > library(xtable)
> > as.string
> function (x, file = "", append = FALSE)
> {
> if (is.null(class(x)))
> switch(data.class(x), character = return(string(x, file,
> append)), numeric = return(string(as.character(x),
> file, append)), stop("Cannot coerse argument to a string"))
> if (class(x) == "string")
> return(x)
> stop("Cannot coerse argument to a string")
^^^^^^
(sic)
> }
>
> Why does the methods package change the class of character vectors?
Because it implements the Green Book (JMC, 1998) where every object has a
class. It just ensures that: it does not change the class of objects
which already have a class (as far as I know).
> Is there a way around this behavior?
Don't use the methods package? More seriously, write and use correct
code which handles classing properly.
-- Brian D. Ripley, ripley@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______________________________________________ R-help@stat.math.ethz.ch mailing list http://www.stat.math.ethz.ch/mailman/listinfo/r-help
This archive was generated by hypermail 2.1.3 : Tue 01 Jul 2003 - 09:11:18 EST