[R] Subsetting a vector using an index with all missing values

[Peter Langfelder]

Ah, thanks, that makes sense.

Peter

On Fri, Jul 1, 2022 at 10:01 PM Bill Dunlap <williamwdunlap using gmail.com> wrote:
>
> This has to do with the mode of the subscript - logical subscripts are repeated to the length of x and integer/numeric ones are not.  NA is logical, NA_integer_ is integer, so we get
>
> > x <- 1:10
> > x[ rep(NA_integer_, 3) ]
> [1] NA NA NA
> > x[ rep(NA, 3) ]
>  [1] NA NA NA NA NA NA NA NA NA NA
>
> -Bill
>
>
> On Fri, Jul 1, 2022 at 8:31 PM Peter Langfelder <peter.langfelder using gmail.com> wrote:
>>
>> Hi all,
>>
>> I stumbled on subsetting behavior that seems counterintuitive and
>> perhaps is a bug. Here's a simple example:
>>
>> > x = 1:10
>> > x[ rep(NA, 3)]
>>  [1] NA NA NA NA NA NA NA NA NA NA
>>
>> I would have expected 3 NAs (the length of the index), not 10 (all
>> values in x). Looked at the documentation for the subsetting operator
>> `[` but found nothing indicating that if the index contains all
>> missing data, the result is the entire vector.
>>
>> I can work around the issue for a general 'index' using a somewhat
>> clunky but straightforward construct along the lines of
>>
>> > index = rep(NA, 3)
>> > x[c(1, index)][-1]
>> [1] NA NA NA
>>
>> but I'm wondering if the behaviour above is intended.
>>
>> Thanks,
>>
>> Peter
>>
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