R devel - Mar 2011 - split(factor, shortGroupVector) gives incorrect results in R 2.12.2

When split's x argument has a class attribute and the
grouping vector, f, is shorter than x then split gives
the wrong result.  It appears to not extend f to the length
of x before doing the split.  E.g.,
   > split(factor(letters[1:3]), "Group one") # expect all 3
elements in
the single group
   $`Group one`
   [1] a
   Levels: a b c
   > split(factor(letters[1:3]), c("Group one", "Group
two")) # expect
warning and Group one should contain "a" and "c".
   $`Group one`
   [1] a
   Levels: a b c

   $`Group two`
   [1] b
   Levels: a b c
We expect the above to act like the similar cases where x is
a character vector
   > split(letters[1:3], "Group one")
   $`Group one`
   [1] "a" "b" "c"

   > split(letters[1:3], c("Group one", "Group two"))
   $`Group one`
   [1] "a" "c"

   $`Group two`
   [1] "b"

   Warning message:
   In split.default(letters[1:3], c("Group one", "Group
two")) :
     data length is not a multiple of split variable

We get a similar problem for other stray classes of x
   > split(structure(letters[1:3],class="no sUch cLaSs"),
c("Group one",
"Group two"))
   $`Group one`
   [1] "a"
 
   $`Group two`
   [1] "b"

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

On Mar 21, 2011, at 17:16 , William Dunlap wrote:
>> split(factor(letters[1:3]), c("Group one", "Group
two"))
Yes, that's a bug (at the very least, it is against documented behavior)

The strong suspicion is that 

    ind <- .Internal(split(seq_along(f), f))

should have seq_along(x) , not f. But would that break for other reasons? 

(It would! Surv() objects to name one case. In general, we seem to be in trouble
if "[" and length() methods are not compatible.)

-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com