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

3 messages · Suharto Anggono Suharto Anggono, Gabriel Becker, Luke Tierney

Original
Suharto Anggono Suharto Anggono
# 
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
Gabriel 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:

            

      
      
      
    

        

      
      
    

        

  
    

      
      
    

  


  


      

    

    
2 days later

    

      
      

        


  

        

      Luke Tierney
    

    

      
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Thanks -- fixed in R-devel and R-3-5-branch.

luke

        
On Fri, 6 Apr 2018, Suharto Anggono Suharto Anggono via R-devel wrote: