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

[Bill Dunlap]

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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