[Rd] Any plans for ALTREP lists (VECSXP)?

[Gabriel Becker]

Hi Kylie,

Is it a list with only numerics in it? (I only see REALSXPs there, but
obviously inspect isn't showing all of them). If so, you could load it up
into one big vector and then also keep partitioning information around.
Bioconductor does this (see ?IRanges::CompressedList ). The potential
benefit here being that the underlying large vector could then be a big
out-of-memory altrep. How helpful this would be depends somewhat on what
you want to do with it, of course, but it is something that comes to mind.

Also, I would expect some overhead but that seems like a lot (without
having done super much in the way of benchmarking). What exactly is
as.altrep doing?

Best,
~G

On Tue, Jul 23, 2019 at 9:54 AM Michael Lawrence via R-devel <
r-devel using r-project.org> wrote:

> Hi Kylie,
>
> As an alternative in the short term, you could consider deriving from
> S4Vector's List class, implementing the getListElement() method to
> lazily create the objects.
>
> Michael
>
> On Tue, Jul 23, 2019 at 9:09 AM Bemis, Kylie <k.bemis using northeastern.edu>
> wrote:
> >
> > Hello,
> >
> > I was wondering if there were any plans for ALTREP lists (VECSXP)?
> >
> > It seems to me that they could be supported in a similar way to how
> ALTSTRING works, with Elt() and Set_elt() methods, or would there be some
> problems with that I’m not seeing due to lists not being atomic vectors?
> >
> > I was taking an approach of converting each list element (of a
> file-based list data structure) to an ALTREP representation to build up an
> “ALTREP list”.
> >
> > This seems fine for shorter lists with large elements, but I noticed
> that for longer lists with smaller elements, this could be far more
> time-consuming than simply reading the entire list into memory and
> returning a non-ALTREP list:
> >
> > > x
> > <34840 length> matter_list :: out-of-memory list
> > (1.1 MB real | 543.3 MB virtual)
> >
> > > system.time(y <- as.list(x))
> >    user  system elapsed
> >   1.116   2.175   5.053
> >
> > > system.time(z <- as.altrep(x))
> >    user  system elapsed
> >  36.295   4.717  41.216
> >
> > > .Internal(inspect(y))
> > @108255000 19 VECSXP g1c7 [MARK,NAM(7)] (len=34840, tl=0)
> >   @7f9044d9fc00 14 REALSXP g1c7 [MARK] (len=1129, tl=0)
> 404.093,404.096,404.099,404.102,404.105,...
> >   @7f9044d25e00 14 REALSXP g1c7 [MARK] (len=890, tl=0)
> 409.924,409.927,409.931,409.934,409.937,...
> >   @7f9044da6000 14 REALSXP g1c7 [MARK] (len=1878, tl=0)
> 400.3,400.303,400.306,400.309,400.312,...
> >   @7f9031a6b000 14 REALSXP g1c7 [MARK] (len=2266, tl=0)
> 402.179,402.182,402.185,402.188,402.191,...
> >   @7f9031a77a00 14 REALSXP g1c7 [MARK] (len=1981, tl=0)
> 403.021,403.024,403.027,403.03,403.033,...
> >   ...
> >
> > > .Internal(inspect(z))
> > @108210000 19 VECSXP g1c7 [MARK,NAM(7)] (len=34840, tl=0)
> >   @7f904eea7660 14 REALSXP g1c0 [MARK,NAM(7)] matter vector (mode=4,
> len=1129, mem=0)
> >   @7f9050347498 14 REALSXP g1c0 [MARK,NAM(7)] matter vector (mode=4,
> len=890, mem=0)
> >   @7f904d286b20 14 REALSXP g1c0 [MARK,NAM(7)] matter vector (mode=4,
> len=1878, mem=0)
> >   @7f904fd38820 14 REALSXP g1c0 [MARK,NAM(7)] matter vector (mode=4,
> len=2266, mem=0)
> >   @7f904c75ce90 14 REALSXP g1c0 [MARK,NAM(7)] matter vector (mode=4,
> len=1981, mem=0)
> >   ...
> >
> > In this situation, it would be much faster and simpler for me to return
> a theoretical ALTREP list that serves SEXP elements on-demand, similar to
> how ALTSTRING seems to be implemented.
> >
> > I don’t know how many other people would get a use out of ALTREP lists,
> but I certainly would.
> >
> > Are there any plans for this?
> >
> > Thanks!
> >
> > ~~~
> > Kylie Ariel Bemis
> > Khoury College of Computer Sciences
> > Northeastern University
> > kuwisdelu.github.io<https://kuwisdelu.github.io>
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >         [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-devel using r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
>
>
>
> --
> Michael Lawrence
> Scientist, Bioinformatics and Computational Biology
> Genentech, A Member of the Roche Group
> Office +1 (650) 225-7760
> michafla using gene.com
>
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