[Rd] [External] ALTREP ALTINTEGER_SUM/MIN/MAX Return Value and Behavior

[iuke-tier@ey m@iii@g oii uiow@@edu]

ALTINTEGER_SUM and friends are _not_ intended for use in package code.
Once we get some time to clean up headers they will no longer be
visible to packages.

Best,

luke

On Tue, 29 Jun 2021, Sebastian Martin Krantz 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]]
>
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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-tierney using uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu