Hi,
On 11/3/09 2:28 PM, William Dunlap wrote:
The following odd call to rep()
gives somewhat random results:
rep(1:4, 1:8, each=2)
I've committed a fix for this to R-devel.
I admit that I had to reread the rep man page as I first thought this
was not a valid call to rep since times (1:8) is longer than x (1:4),
but closer reading of the man page says:
> If times is a vector of the same length as x (after replication
> by each), the result consists of x[1] repeated times[1] times,
> x[2] repeated times[2] times and so on.
So the expected result is the same as rep(rep(1:4, each=2), 1:8).
valgrind says that the C code is using uninitialized data:
rep(1:4, 1:8, each=2)
==26459== Conditional jump or move depends on uninitialised value(s)
==26459== at 0x80C557D: integerSubscript (subscript.c:408)
==26459== by 0x80C5EDC: Rf_vectorSubscript (subscript.c:658)
A little investigation seems to suggest that the problem is originating
earlier. Debugging in seq.c:do_rep I see the following:
> rep(1:4, 1:8, each=2)
Breakpoint 1, do_rep (call=0x102de0068, op=<value temporarily
unavailable, due to optimizations>, args=<value temporarily unavailable,
due to optimizations>, rho=0x1018829f0) at
/Users/seth/src/R-devel-all/src/main/seq.c:434
434 ans = do_subset_dflt(R_NilValue, R_NilValue, list2(x, ind),
rho);
(gdb) p Rf_PrintValue(ind)
[1] 1 1 1 2 2 2
[7] 2 2 2 2 3 3
[13] 3 3 3 3 3 3
[19] 3 3 3 4 4 4
[25] 4 4 4 4 4 4
[31] 4 4 4 4 4 4
[37] 44129344 1 44129560 1 44129776 1
[43] 44129992 1 44099592 1 44099808 1
[49] 44100024 1 44100456 1 2724144 3801089
[55] -536870733 0 54857992 1 22275728 1
[61] 2724144 1 34 1 44100744 1
[67] 44100960 1 44101176 1 43652616 1
$2 = void
(gdb) c
Continuing.
Error: only 0's may be mixed with negative subscripts
The patch I applied adjusts how the index vector length is computed when
times has length more than one.
+ seth
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