[datatable-help] logicals in datatable i

[Matthew Dowle]

Yes indeed it's intended and there is this in FAQ 2.17 (differences
between DF and DT) : 

 "DT[NA] returns 1 row of NA, but DF[NA] returns
a copy of DF containing NA throughout. The
symbol NA is type logical in
R, and is therefore recycled by [.data.frame. Intention was
probably
DF[NA_integer_]. [.data.table does this automatically for
convenience."

I see what you mean Gabor about that sentence in
?data.table. Thanks, will improve that wording.

Matthew

On 24.05.2013
17:40, Arunkumar Srinivasan wrote: 

> Gabor, 
> Not sure if this is
intended, but the there's a code that explicitly assigns NA_integer_ if
`i` is NA in `[.data.table`: 
> 
> if (is.logical(i)) { 
> if
(identical(i, NA)) 
> i = NA_integer_ 
> else i[is.na(i)] = FALSE 
> }

> So, if `i` is JUST `NA`, then it's replaced with NA_integer_. If
there are more than 1 element and i has NA in them, they are replaced
with FALSE. 
> For ex: doing 
> DT1[as.logical(c(NA, NA))] 
> would
result in recycling and lead to a 0 rows and 1 column empty data.table.

> 
> Arun 
> 
> On Friday, May 24, 2013 at 6:29 PM, Gabor Grothendieck
wrote: 
> 
>> The ?data.table page describing arg i says: 
>> "integer
and logical vectors work the same way they do in 
>> [.data.frame. Other
than NAs in logical i are treated as FALSE and a 
>> single NA logical
is not recycled to match the number of rows, as it 
>> is
in[.data.frame." 
>> however, I get this: 
>> 
>>>
packageVersion("data.table")
>> 
>> [1] '1.8.9' 
>> 
>>> DT1 <-
data.table(a = 1:5) 
>>> DT1[as.logical(NA)]
>> 
>> a 
>> 1: NA 
>> so
it seems that if there is a single logical NA it not only is not 
>>
recycled but it also is not regarded as FALSE (whereas the quoted 
>>
statement seems to say a logical NA is regarded as FALSE in all 
>>
cases). 
>> Is this intended? 
>> -- 
>> Statistics & Software
Consulting 
>> GKX Group, GKX Associates Inc. 
>> tel: 1-877-GKX-GROUP

>> email: ggrothendieck at gmail.com [1] 
>>
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