[R] Is there a hash data structure for R

[Bill Dunlap]

Note that an environment carries a hash table with it, while a named list
does not.  I think that looking up an entry in a list causes a hash table
to be created and thrown away.  Here are some timings involving setting and
getting various numbers of entries in environments and lists.  The times
are roughly linear in n for environments and quadratic for lists.

> vapply(1e3 * 2 ^ (0:6), f, L=new.env(parent=emptyenv()),
FUN.VALUE=NA_real_)
[1] 0.00 0.00 0.00 0.02 0.03 0.06 0.15
> vapply(1e3 * 2 ^ (0:6), f, L=list(), FUN.VALUE=NA_real_)
[1]  0.01  0.03  0.15  0.53  2.66 13.66 56.05
> f
function(n, L, V = sprintf("V%07d", sample(n, replace=TRUE))) {
    system.time(for(v in V)L[[v]]<-c(L[[v]],v))["elapsed"]
}

Note that environments do not allow an element named "" (the empty string).

Elements named NA_character_ are treated differently in environments and
lists, neither of which is great.  You may want your hash table functions
to deal with oddball names explicitly.

-Bill

On Tue, Nov 2, 2021 at 8:52 AM Andrew Simmons <akwsimmo using gmail.com> wrote:

> If you're thinking about using environments, I would suggest you initialize
> them like
>
>
> x <- new.env(parent = emptyenv())
>
>
> Since environments have parent environments, it means that requesting a
> value from that environment can actually return the value stored in a
> parent environment (this isn't an issue for [[ or $, this is exclusively an
> issue with assign, get, and exists)
> Or, if you've already got your values stored in a list that you want to
> turn into an environment:
>
>
> x <- list2env(listOfValues, parent = emptyenv())
>
>
> Hope this helps!
>
>
> On Tue, Nov 2, 2021, 06:49 Yonghua Peng <yong using pobox.com> wrote:
>
> > But for data.frame the colnames can be duplicated. Am I right?
> >
> > Regards.
> >
> > On Tue, Nov 2, 2021 at 6:29 PM Jan van der Laan <rhelp using eoos.dds.nl>
> wrote:
> >
> > >
> > > True, but in a lot of cases where a python user might use a dict an R
> > > user will probably use a list; or when we are talking about arrays of
> > > dicts in python, the R solution will probably be a data.frame (with
> each
> > > dict field in a separate column).
> > >
> > > Jan
> > >
> > >
> > >
> > >
> > > On 02-11-2021 11:18, Eric Berger wrote:
> > > > One choice is
> > > > new.env(hash=TRUE)
> > > > in the base package
> > > >
> > > >
> > > >
> > > > On Tue, Nov 2, 2021 at 11:48 AM Yonghua Peng <yong using pobox.com> wrote:
> > > >
> > > >> I know this is a newbie question. But how do I implement the hash
> > > structure
> > > >> which is available in other languages (in python it's dict)?
> > > >>
> > > >> I know there is the list, but list's names can be duplicated here.
> > > >>
> > > >>> x <- list(x=1:5,y=month.name,x=3:7)
> > > >>
> > > >>> x
> > > >>
> > > >> $x
> > > >>
> > > >> [1] 1 2 3 4 5
> > > >>
> > > >>
> > > >> $y
> > > >>
> > > >>   [1] "January"   "February"  "March"     "April"     "May"
> >  "June"
> > > >>
> > > >>   [7] "July"      "August"    "September" "October"   "November"
> > > "December"
> > > >>
> > > >>
> > > >> $x
> > > >>
> > > >> [1] 3 4 5 6 7
> > > >>
> > > >>
> > > >>
> > > >> Thanks a lot.
> > > >>
> > > >>          [[alternative HTML version deleted]]
> > > >>
> > > >> ______________________________________________
> > > >> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > > >> https://stat.ethz.ch/mailman/listinfo/r-help
> > > >> PLEASE do read the posting guide
> > > >> http://www.R-project.org/posting-guide.html
> > > >> and provide commented, minimal, self-contained, reproducible code.
> > > >>
> > > >
> > > >       [[alternative HTML version deleted]]
> > > >
> > > > ______________________________________________
> > > > R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > > PLEASE do read the posting guide
> > > http://www.R-project.org/posting-guide.html
> > > > and provide commented, minimal, self-contained, reproducible code.
> > > >
> > >
> > > ______________________________________________
> > > R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > PLEASE do read the posting guide
> > > http://www.R-project.org/posting-guide.html
> > > and provide commented, minimal, self-contained, reproducible code.
> > >
> >
> >         [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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