Peter Langfelder
2022-Jul-02 03:30 UTC
[R] Subsetting a vector using an index with all missing values
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
Bill Dunlap
2022-Jul-02 05:01 UTC
[R] Subsetting a vector using an index with all missing values
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 at 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 > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >[[alternative HTML version deleted]]