[Rd] subsetting matrix by subscript=0,x silently skips.

[Hin-Tak Leung]

(I have taken off r-bug@, as multiple e-mails hitting r-bug@ probably 
will result in multiple bug reports, knowing most mail server will
retry)

Tony Plate wrote:
> The help page for "[" says:
> 
> A third form of indexing is via a numeric matrix with the one column for 
> each dimension: each row of the index matrix then selects a single 
> element of the array, and the result is a vector. Negative indices are 
> not allowed in the index matrix. NA and zero values are allowed: rows of 
> an index matrix containing a zero are ignored, whereas rows containing 
> an NA produce an NA in the result.
> 
> So, I think it is behaving as documented.

Hmm, fair enough. I guess the NA one make sense (In R as a rule,
NA in, NA out), but I am not sure I understand or agree with
the rationale of silently ignoring (0,x) and (x,0)'s. Any reason for that?

HTL

> Hin-Tak Leung wrote:
>> (e-mailing to R-bugs is intentional - the web itnerface seems to
>> be down)
>>
>>  > a<- cbind(c(1,2), c(3,4))
>>  > a
>>       [,1] [,2]
>> [1,]    1    3
>> [2,]    2    4
>>
>>  > a[cbind(c(2,2), c(2,1))]
>> [1] 4 2
>>  > a[cbind(c(2,3), c(2,1))]
>> Error: subscript out of bounds
>>  > a[cbind(c(2,-1), c(2,1))]
>> Error: negative values are not allowed in a matrix subscript
>>  > a[cbind(c(2,0), c(2,1))]
>> [1] 4
>>
>> Am somewhat surprised that 2,0 just silently skip over and doesn't
>> throw an error like 2,0 and 2,-1 . Surely it should throw
>> an error about subscript should be >= 1?
>>
>>
>>
>>  > sessionInfo()
>> R version 2.4.1 (2006-12-18)
>> i686-redhat-linux-gnu
>>
>> locale:
>> LC_CTYPE=en_GB.UTF-8;LC_NUMERIC=C;LC_TIME=en_GB.UTF-8;LC_COLLATE=en_GB.UTF-8;LC_MONETARY=en_GB.UTF-8;LC_MESSAGES=en_GB.UTF-8;LC_PAPER=en_GB.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_GB.UTF-8;LC_IDENTIFICATION=C 
>>
>>
>> attached base packages:
>> [1] "splines"   "stats"     "graphics"  "grDevices" "utils"     
>> "datasets"
>> [7] "methods"   "base"
>>
>> other attached packages:
>> snpMatrix  survival
>>    "1.0.4"    "2.30"
>>  >
>>
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>>
>