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

[Ebert,Timothy Aaron]

That nicely explains the difference in outcome between 
x[rep(TRUE,3)]
x[rep("TRUE",3)]


I do not quite get it.
x<-1:10
x[rep(x<2,3)]
[1] 1 NA NA
The length is three

but
x[rep(x>2,3)]
[1] 3  4  5  6  7  8  9  10  NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
The length is 24

Tim
-----Original Message-----
From: R-help <r-help-bounces using r-project.org> On Behalf Of Peter Langfelder
Sent: Saturday, July 2, 2022 2:19 AM
To: Bill Dunlap <williamwdunlap using gmail.com>
Cc: r-help <r-help using r-project.org>
Subject: Re: [R] Subsetting a vector using an index with all missing values

[External Email]

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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