Call the R sum() function, either before going to C code or by calling
back into R. You may only want to do this if the vector is long enough
for e possible savings to be worth while.
On Tue, 29 Jun 2021, Sebastian Martin Krantz wrote:
Thanks both. Is there a suggested way I can get this speedup in a package?
Or just leave it for now?
Thanks also for the clarification Bill. The issue I have with that is that
in my C code ALTREP(x) evaluates to true even after adding and removing
dimensions (otherwise it would be handled by the normal sum method and I’d
be fine).
When you use a longer vector
Also .Internal(inspect(x)) still shows the compact
representation.
A different representation (wrapper around a compact sequence).
Best,
luke
-Sebastian
On Tue 29. Jun 2021 at 19:43, Bill Dunlap <williamwdun...@gmail.com> wrote:
Adding the dimensions attribute takes away the altrep-ness. Removing
dimensions
does not make it altrep. E.g.,
a <- 1:10
am <- a ; dim(am) <- c(2L,5L)
amn <- am ; dim(amn) <- NULL
.Call("is_altrep", a)
[1] TRUE
.Call("is_altrep", am)
[1] FALSE
.Call("is_altrep", amn)
[1] FALSE
where is_altrep() is defined by the following C code:
#include <R.h>
#include <Rinternals.h>
SEXP is_altrep(SEXP x)
{
return Rf_ScalarLogical(ALTREP(x));
}
-Bill
On Tue, Jun 29, 2021 at 8:03 AM Sebastian Martin Krantz <
sebastian.kra...@graduateinstitute.ch> wrote:
Hello together, I'm working on some custom (grouped, weighted) sum, min
and
max functions and I want them to support the special case of plain integer
sequences using ALTREP. I thereby encountered some behavior I cannot
explain to myself. The head of my fsum C function looks like this (g is
optional grouping vector, w is optional weights vector):
SEXP fsumC(SEXP x, SEXP Rng, SEXP g, SEXP w, SEXP Rnarm) {
int l = length(x), tx = TYPEOF(x), ng = asInteger(Rng),
narm = asLogical(Rnarm), nprotect = 1, nwl = isNull(w);
if(ALTREP(x) && ng == 0 && nwl) {
switch(tx) {
case INTSXP: return ALTINTEGER_SUM(x, (Rboolean)narm);
case LGLSXP: return ALTLOGICAL_SUM(x, (Rboolean)narm);
case REALSXP: return ALTLOGICAL_SUM(x, (Rboolean)narm);
default: error("ALTREP object must be integer or real typed");
}
}
// ...
}
when I let x <- 1:1e8, fsum(x) works fine and returns the correct value.
If
I now make this a matrix dim(x) <- c(1e2, 1e6) and subsequently turn this
into a vector again, dim(x) <- NULL, fsum(x) gives NULL and a warning
message 'converting NULL pointer to R NULL'. For functions fmin and fmax
(similarly defined using ALTINTEGER_MIN/MAX), I get this error right away
e.g. fmin(1:1e8) gives NULL and warning 'converting NULL pointer to R
NULL'. So what is going on here? What do these functions return? And how
do
I make this a robust implementation?
Best regards,
Sebastian Krantz
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--
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa Phone: 319-335-3386
Department of Statistics and Fax: 319-335-3017
Actuarial Science
241 Schaeffer Hall email: luke-tier...@uiowa.edu
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
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