R devel - Mar 2007 - (PR#9578) rbind.data.frame reacts on levels without

In your data frames, 'y' is a category and the following comment in the
code makes clear this is deliberate.

 		    if( !is.null(levels(xj)) ) {
 			all.levs[[j]] <- levels(xj)
                         facCol[j] <- TRUE # turn categories into factors
                     } else facCol[j] <- is.factor(xj)

The behaviour is compatible with S apart from the comment in the R help 
page.  That categories are promoted to factors is consistent with the help 
for 'category'.

It is not a bug, but the help page could say what happens for categories.

On Fri, 23 Mar 2007, Lutz Prechelt wrote:
> I am sorry.
> Here is a minimal example:
>
> a=data.frame(x=c(1:3),y=unclass(factor(c(5:7))))
> b=data.frame(x=c(11:13),y=unclass(factor(c(7:9))))
> rbind(a,b)
>
>  Lutz Prechelt
>
>
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
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