[R] detecting if a variable has changed

[Bert Gunter]

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 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
>>
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>>
>
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>
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.