[R] detecting if a variable has changed

[Neal H. Walfield]

On Sun, 05 Jun 2016 19:34:38 +0200,
Bert Gunter wrote:
> This help thread suggested a question to me:
> 
> Is there a function in some package that efficiently (I.e. O(log(n)) )
> inserts a single new element into the correct location in an
> already-sorted vector? My assumption here is that doing it via sort()
> is inefficient, but maybe that is incorrect. Please correct me if so.

I think data.table will do this if the the column is marked
appropriately.

> I realize that it would be straightforward to write such a function,
> but I just wondered if it already exists. My google & rseek searches
> did not succeed, but maybe I used the wrong keywords.
> 
> Cheers,
> Bert
> 
> 
> Bert Gunter
> 
> "The trouble with having an open mind is that people keep coming along
> and sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
> 
> 
> On Sun, Jun 5, 2016 at 9:47 AM, William Dunlap via R-help
> <r-help at r-project.org> wrote:
> > I don't know what you mean by "without having to use any special
> > interfaces", but "reference classes" will do what I think you want.  E.g.,
> > the following makes a class called 'SortedNumeric' that only sorts the
> > vector when you want to get its value, not when you append values.  It
> > stores the sorted vector so it does not get resorted each time you ask for
> > it.
> >
> > SortedNumeric <- setRefClass("sortedNumeric",
> >             fields = list(
> >                 fData = "numeric",
> >                 fIsUnsorted = "logical"),
> >             methods = list(
> >                 initialize = function(Data = numeric(), isUnsorted = TRUE) {
> >                     fData <<- Data
> >                     stopifnot(is.logical(isUnsorted),
> >                               length(isUnsorted)==1,
> >                               !is.na(isUnsorted))
> >                     fIsUnsorted <<- isUnsorted
> >                 },
> >                 getData = function() {
> >                     if (isUnsorted) {
> >                         fData <<- sort(fData)
> >                         fIsUnsorted <<- FALSE
> >                     }
> >                     fData
> >                 },
> >                 appendData = function(newEntries) {
> >                     fData <<- c(fData, newEntries)
> >                     fIsUnsorted <<- TRUE
> >                 }
> >             ))
> >
> > Use it as:
> >
> >> x <- SortedNumeric$new()
> >> x$appendData(c(4,2,5))
> >> x$appendData(c(1,8,9))
> >> x
> > Reference class object of class "sortedNumeric"
> > Field "fData":
> > [1] 4 2 5 1 8 9
> > Field "fIsUnsorted":
> > [1] TRUE
> >> x$getData()
> > [1] 1 2 4 5 8 9
> >> x
> > Reference class object of class "sortedNumeric"
> > Field "fData":
> > [1] 1 2 4 5 8 9
> > Field "fIsUnsorted":
> > [1] FALSE
> >
> >
> > Outside of base R, I think the R6 package gives another approach to this.
> >
> >
> > Bill Dunlap
> > TIBCO Software
> > wdunlap tibco.com
> >
> > On Sun, Jun 5, 2016 at 6:53 AM, Neal H. Walfield <neal at walfield.org> wrote:
> >
> >> Hi,
> >>
> >> I have a huge list.  Normally it is sorted, but I want to be able to
> >> add elements to it without having to use any special interfaces and
> >> then sort it on demand.  My idea is to use something like weak
> >> references combined with attributes.  Consider:
> >>
> >>   # Initialization.
> >>   l = as.list(1:10)
> >>   # Note that it is sorted.
> >>   attr(l, 'sorted') = weakref(l)
> >>
> >>   # Modify the list.
> >>   l = append(l, 1:3)
> >>
> >>   # Check if the list is still sorted.  (I use identical here, but it
> >>   # probably too heavy weight: I just need to compare the addresses.)
> >>   if (! identical(l, attr(l, 'sorted'))) {
> >>     l = sort(unlist(l))
> >>     attr(l, 'sorted') = weakref(l)
> >>   }
> >>   # Do operation that requires sorted list.
> >>   ...
> >>
> >> This is obviously a toy example.  I'm not actually sorting integers
> >> and I may use a matrix instead of a list.
> >>
> >> I've read:
> >>
> >>   http://www.hep.by/gnu/r-patched/r-exts/R-exts_122.html
> >>   http://homepage.stat.uiowa.edu/~luke/R/references/weakfinex.html
> >>
> >> As far as I can tell, weakrefs are only available via the C API.  Is
> >> there a way to do what I want in R without resorting to C code?  Is
> >> what I want to do better achieved using something other than weakrefs?
> >>
> >> Thanks!
> >>
> >> :) Neal
> >>
> >> ______________________________________________
> >> R-help at 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 at 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.
>