[Rd] Faster sorting algorithm...

[Morgan Morgan]

My apologies to Professor Neal.
Thank you for correcting me.
Best regards
Morgan


On Mon, 22 Mar 2021, 05:05 , <frederik using ofb.net> wrote:

> I think it is "Professor Neal" :)
>
> I also appreciate the pqR comparisons.
>
> On Wed, Mar 17, 2021 at 09:23:15AM +0000, Morgan Morgan wrote:
> >Thank you Neal. This is interesting. I will have a look at pqR.
> >Indeed radix only does C collation, I believe that is why it is not the
> >default choice for character ordering and sorting.
> >Not sure but I believe it can help address the following bugzilla item:
> >https://bugs.r-project.org/bugzilla/show_bug.cgi?id=17400
> >
> >On the same topic of collation, there is an experimental sorting function
> >"psort" in package kit that might help address this issue.
> >
> >> library(kit)
> >Attaching kit 0.0.7 (OPENMP enabled using 1 thread)
> >> x <- c("b","A","B","a","\xe4")
> >> Encoding(x) <- "latin1"
> >> identical(psort(x, c.locale=FALSE), sort(x))
> >[1] TRUE
> >> identical(psort(x, c.locale=TRUE), sort(x, method="radix"))
> >[1] TRUE
> >
> >Coming back to the topic of fsort, I have just finished the implementation
> >for double, integer, factor and logical.
> >The implementation takes into account NA, Inf.. values. Values can be
> >sorted in a decreasing order or increasing order.
> >Comparing benchmark with the current implementation in data.table, it is
> >currently over 30% faster.
> >There might bugs but I am sure performance can be further improved as I
> did
> >not really try hard.
> >If there is interest in both the implementation and cross community
> >sharing, please let know....
> >
> >Best regards,
> >Morgan
> >
> >On Wed, 17 Mar 2021, 00:37 Radford Neal, <radford using cs.toronto.edu> wrote:
> >
> >> Those interested in faster sorting may want to look at the merge sort
> >> implemented in pqR (see pqR-project.org).  It's often used as the
> >> default, because it is stable, and does different collations, while
> >> being faster than shell sort (except for small vectors).
> >>
> >> Here are examples, with timings, for pqR-2020-07-23 and R-4.0.2,
> >> compiled identically:
> >>
> >> -----------------------------
> >> pqR-2020-07-23 in C locale:
> >>
> >> > set.seed(1)
> >> > N <- 1000000
> >> > x <- as.character (sample(N,N,replace=TRUE))
> >> > print(system.time (os <- order(x,method="shell")))
> >>    user  system elapsed
> >>   1.332   0.000   1.334
> >> > print(system.time (or <- order(x,method="radix")))
> >>    user  system elapsed
> >>   0.092   0.004   0.096
> >> > print(system.time (om <- order(x,method="merge")))
> >>    user  system elapsed
> >>   0.363   0.000   0.363
> >> > print(identical(os,or))
> >> [1] TRUE
> >> > print(identical(os,om))
> >> [1] TRUE
> >> >
> >> > x <- c("a","~")
> >> > print(order(x,method="shell"))
> >> [1] 1 2
> >> > print(order(x,method="radix"))
> >> [1] 1 2
> >> > print(order(x,method="merge"))
> >> [1] 1 2
> >>
> >> -----------------------------
> >> R-4.0.2 in C locale:
> >>
> >> > set.seed(1)
> >> > N <- 1000000
> >> > x <- as.character (sample(N,N,replace=TRUE))
> >> > print(system.time (os <- order(x,method="shell")))
> >>    user  system elapsed
> >>   2.381   0.004   2.387
> >> > print(system.time (or <- order(x,method="radix")))
> >>    user  system elapsed
> >>   0.138   0.000   0.137
> >> > #print(system.time (om <- order(x,method="merge")))
> >> > print(identical(os,or))
> >> [1] TRUE
> >> > #print(identical(os,om))
> >> >
> >> > x <- c("a","~")
> >> > print(order(x,method="shell"))
> >> [1] 1 2
> >> > print(order(x,method="radix"))
> >> [1] 1 2
> >> > #print(order(x,method="merge"))
> >>
> >> ------------------------------------
> >> pqR-2020-07-23 in fr_CA.utf8 locale:
> >>
> >> > set.seed(1)
> >> > N <- 1000000
> >> > x <- as.character (sample(N,N,replace=TRUE))
> >> > print(system.time (os <- order(x,method="shell")))
> >> utilisateur     système      écoulé
> >>       2.960       0.000       2.962
> >> > print(system.time (or <- order(x,method="radix")))
> >> utilisateur     système      écoulé
> >>       0.083       0.008       0.092
> >> > print(system.time (om <- order(x,method="merge")))
> >> utilisateur     système      écoulé
> >>       1.143       0.000       1.142
> >> > print(identical(os,or))
> >> [1] TRUE
> >> > print(identical(os,om))
> >> [1] TRUE
> >> >
> >> > x <- c("a","~")
> >> > print(order(x,method="shell"))
> >> [1] 2 1
> >> > print(order(x,method="radix"))
> >> [1] 1 2
> >> > print(order(x,method="merge"))
> >> [1] 2 1
> >>
> >> ------------------------------------
> >> R-4.0.2 in fr_CA.utf8 locale:
> >>
> >> > set.seed(1)
> >> > N <- 1000000
> >> > x <- as.character (sample(N,N,replace=TRUE))
> >> > print(system.time (os <- order(x,method="shell")))
> >> utilisateur     système      écoulé
> >>       4.222       0.016       4.239
> >> > print(system.time (or <- order(x,method="radix")))
> >> utilisateur     système      écoulé
> >>       0.136       0.000       0.137
> >> > #print(system.time (om <- order(x,method="merge")))
> >> > print(identical(os,or))
> >> [1] TRUE
> >> > #print(identical(os,om))
> >> >
> >> > x <- c("a","~")
> >> > print(order(x,method="shell"))
> >> [1] 2 1
> >> > print(order(x,method="radix"))
> >> [1] 1 2
> >> > #print(order(x,method="merge"))
> >>
> >>
> >> pqR is faster in all the tests, but more relevant to this discussion
> >> is that the "merge" method is substantially faster than "shell" for
> >> these character vectors with a million elements, while retaining the
> >> stability and collation properties of "shell" (whereas "radix" only
> >> does C collation).
> >>
> >> It would probably not be too hard to take the merge sort code from pqR
> >> and use it in R core's implementation.
> >>
> >> The merge sort in pqR doesn't exploit parallelism at the moment, but
> >> merge sort is potentially quite parallelizable (though I think the
> >> storage allocation strategy I use would have to be modified).
> >>
> >> Regards,
> >>
> >>    Radford Neal
> >>
> >> ______________________________________________
> >> R-devel using r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-devel
> >>
> >
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> >
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> >
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