[Rd] R Language Definition: Subsetting matrices with negative indices is *not* an error

[Bert Gunter]

Ah, the woes of English word order -- even this native English speaker
frequently gets messed up!

(but maybe I'm just a bear of little brain).

Best,
Bert

Bert Gunter
Genentech Nonclinical Biostatistics
(650) 467-7374

"Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom."
Clifford Stoll




On Sat, May 9, 2015 at 1:33 PM, Henrik Bengtsson
<henrik.bengtsson at ucsf.edu> wrote:
> On Sat, May 9, 2015 at 12:55 AM, peter dalgaard <pdalgd at gmail.com> wrote:
>>
>>> On 09 May 2015, at 02:53 , Henrik Bengtsson <henrik.bengtsson at ucsf.edu> wrote:
>>>
>>> Hi,
>>>
>>> I spotted what looks like another(*) mistake in 'R Language
>>> Definition' on how subsetting should work.  In Section 'Indexing
>>> matrices and arrays'
>>> [http://cran.r-project.org/doc/manuals/r-release/R-lang.html#Indexing-matrices-and-arrays]
>>> one can read
>>>
>>>   "Negative indices are not allowed in indexing matrices."
>>
>> Parse error: I believe that this is intended to mean
>>
>> "Indexing matrices may not contain negative indices"
>>
>> not
>>
>> "You cannot use negative indices when indexing matrices".
>>
>> This is consistent with the help page:
>>
>> "
>>      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.
>> "
>>
>> Rephrasing would seem to be in order....
>
> Ah... definitely a "parse error" (I read it as a new paragraph).  I
> second rephrasing this; your ""Indexing matrices may not contain
> negative indices" is non-ambiguous.
>
> Thanks Peter
>
> /Henrik
>
>>
>> -pd
>>
>>>
>>> but this is not true, e.g.
>>>
>>>> x <- matrix(1:12, nrow=4)
>>>> x
>>>     [,1] [,2] [,3]
>>> [1,]    1    5    9
>>> [2,]    2    6   10
>>> [3,]    3    7   11
>>> [4,]    4    8   12
>>>
>>>> x[c(-2,-4),]
>>>     [,1] [,2] [,3]
>>> [1,]    1    5    9
>>> [2,]    3    7   11
>>>
>>> /Henrik
>>>
>>> (*) https://stat.ethz.ch/pipermail/r-devel/2015-May/071091.html [docs
>>> have been fixed]
>>>
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>> --
>> Peter Dalgaard, Professor,
>> 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
>>
>>
>>
>>
>>
>>
>>
>>
>
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