[R] Bug in levels() function?

[Groot, Philip de]

Hello all,
 
I am not sure whether it actually is a bug, but it is not the behaviour I would expect. Please consider this:
 
>Sibships
 [1] Patient_2400 Patient_2400 Patient_345  Patient_345  Patient_8901
 [6] Patient_8901 Patient_4008 Patient_4008 Patient_7991 Patient_7991
[11] Patient_8353 Patient_8353 Patient_1212 Patient_1212 Patient_2168
[16] Patient_2168 Patient_2760 Patient_2760 Patient_4726 Patient_4726
[21] Patient_6699 Patient_6699 Patient_7641 Patient_7641 Patient_8263
[26] Patient_8263 Patient_1389 Patient_1389 Patient_1618 Patient_1618
[31] Patient_2410 Patient_2410 Patient_2612 Patient_2612 Patient_2721
[36] Patient_2721 Patient_5053 Patient_5053 Patient_8458 Patient_8458
[41] Patient_211  Patient_211  Patient_9004 Patient_9004 Patient_3423
[46] Patient_3423 Patient_7413 Patient_7413 Patient_7815 Patient_7815
[51] Patient_9232 Patient_9232 Patient_2267 Patient_2267 Patient_468
[56] Patient_468
28 Levels: Patient_1212 Patient_1389 Patient_1618 Patient_211 ... Patient_9232
 
>Comparison_Indices
 [1]  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE
[13] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
[25] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
[37] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE  TRUE  TRUE
[49] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
 
> Sibships[Comparison_Indices]
[1] Patient_2400 Patient_2400 Patient_345  Patient_345  Patient_8901
[6] Patient_8901 Patient_7413 Patient_7413
28 Levels: Patient_1212 Patient_1389 Patient_1618 Patient_211 ... Patient_9232

The problem with this last command is that I would expect 4 levels (because only 8 "Comparison_Indices" are true, which is equal to 4 sibships. So: levels() does not take array indices into account or stated otherwise: if you use a subset in an array (vector), the levels() are not properly updated (to my opinion).
 
What I additionally found is the following:
> small_test <- factor(x=c("a", "b", "c"))
> typeof(small_test)
[1] "integer"

The same happens to the Sibships that I defined as a factor? Why is it of type integer?
 
This is the version() output:
> version
               _
platform       x86_64-unknown-linux-gnu
arch           x86_64
os             linux-gnu
system         x86_64, linux-gnu
status
major          2
minor          6.1
year           2007
month          11
day            26
svn rev        43537
language       R
version.string R version 2.6.1 (2007-11-26)
>
 
So: should I submit a Bug report?
 
Regards,
 
Dr. Philip de Groot
Wageningen University