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, <radf...@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@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
[[alternative HTML version deleted]]
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
