[R] detecting if a variable has changed

[Neal H. Walfield]

Hi,

This looks more or less what I'm looking for!  Thanks!

:) Neal

On Sun, 05 Jun 2016 18:47:11 +0200,
William Dunlap wrote:
> 
> [1  <text/plain; UTF-8 (7bit)>]
> [2  <text/html; UTF-8 (quoted-printable)>]
> 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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