[Rd] Part of fastpass in 'sort.list' can make sorting unstable

[Gabe Becker]

Thanks for catching this. This is easy to take out without touching the
rest of the machinery. It also wouldn't be too hard to write a
still-faster-but-not-quite-as-much-path which correctly reverses the
sortedness of a sorted vector that includes ties. My suspicion, without
being the one who will ultimately make that decision, is that that wouldn't
go into 3.5.0 though.

Best,
~G

On Fri, Apr 6, 2018 at 3:03 PM, Suharto Anggono Suharto Anggono via R-devel
<r-devel at r-project.org> wrote:

> In the code of functions 'order' and 'sort.list' in R 3.5.0 alpha (in
> https://svn.r-project.org/R/branches/R-3-5-branch/src/
> library/base/R/sort.R), in "fastpass, take advantage of ALTREP metadata",
> there is "try the reverse since that's easy too...". If it succeeds, ties
> are reordered, violating stability of sorting.
>
> Example:
> x <- sort(c(1, 1, 3))
> x  # 1 1 3
> sort.list(x, decreasing=TRUE)  # should be 3 1 2
>
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>


-- 
Gabriel Becker, Ph.D
Scientist
Bioinformatics and Computational Biology
Genentech Research

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