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

Gabe Becker becker.gabe at gene.com
Sat Apr 7 00:43:57 CEST 2018

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.


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
Bioinformatics and Computational Biology
Genentech Research

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