It depends on the size. For a larger vector adding dim will create a wrapper ALTREP.
Currently the wrapper does not try to use the payload's sum method; this could be added. Best, luke On Tue, 29 Jun 2021, Bill Dunlap 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 [[alternative HTML version deleted]] ______________________________________________ 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
-- 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 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
