List seems to drop empty levels of factors when containin g them

I don't get the same result, do you have a package loaded that would change
the default behavior (such as Hmisc)?

list(grp.1)

[[1]]
[1] 1 2
Levels: 1 2

list(grp.1[mask])

[[1]]
[1] 1
Levels: 1 2

library(Hmisc)

<<snip>>

list(grp.1[mask])

[[1]]
[1] 1
Levels: 1

--Matt

version

         _              
platform i386-pc-mingw32
arch     i386           
os       mingw32        
system   i386, mingw32  
status                  
major    2              
minor    0.0            
year     2004           
month    10             
day      04             
language R             


-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch]On Behalf Of Andrew Robinson
Sent: Tuesday, November 09, 2004 19:44 PM
To: R-Help Discussion
Cc: Andrew Robinson
Subject: [R] List seems to drop empty levels of factors when containing
them


Greetings R community,

I am curious about the following behaviour: if I define a factor, and
then store a subset of it in a list, the stored version seems to drop
levels that were not included in the subset.  E.g. ..

mask <- c(T, F)
grp.1 <- factor(c(1,2))
list(grp.1)

[[1]]
[1] 1 2
Levels: 1 2

list(grp.1[mask])

[[1]]
[1] 1
Levels: 1

It is as though the list were redefining the factor and dropping
empty levels.  I would like to keep them (I am using the list for a
two-dimensional tapply). Is there any way to avoid this?

I'm using R 2.0.0 on FreeBSD 5.2.1.

Thanks,

Andrew
-- 
Andrew Robinson                      Ph: 208 885 7115
Department of Forest Resources       Fa: 208 885 6226
University of Idaho                  E : andrewr at uidaho.edu
PO Box 441133                        W : http://www.uidaho.edu/~andrewr
Moscow ID 83843                      Or: http://www.biometrics.uidaho.edu
No statement above necessarily represents my employer's opinion.