[R] Copy on assignment and .Internal(inspect())

[Carlos Pita]

Here's another approach using the sampling profiler:

prof <- function() {
  Rprof(memory.profiling=T, interval=0.001)
  replicate(100, f())
  Rprof(NULL)
  summaryRprof(memory = "stats")
}

f <- function() {
  x = seq(1000)
  for(i in seq(1000)) {
    x[i] <- x[i] + 1
  }
}

prof()

=>

index: "prof":"replicate"

     vsize.small  max.vsize.small      vsize.large  max.vsize.large
            1938           285003             1629           210990

           nodes        max.nodes     duplications tot.duplications
          265805         13949348                7             1703

         samples
             251

Average duplications are just 9 for 1000 executions of x[i] <- x[i] +
1. A lot of optimization seems to be going on!

How do I make sense of the output listed in my previous post, then?

Best regards
--
Carlos


On Thu, Jan 24, 2013 at 12:38 AM, Carlos Pita <carlosjosepita at gmail.com> wrote:
> Hi,
>
> I would like to know if it's ok to use .Internal(inspect(x)) in order
> to detect vector copying.
>
> Take for example the following silly code:
>
>   f <- function() {
>   x = seq(10)
>   print(.Internal(inspect(x)))
>   for(i in seq(10)) {
>     x[i] <- x[i] + 1
>     print(.Internal(inspect(x)))
>   }
> }
>
> The output of f() was:
>
> @bd7acf0 13 INTSXP g0c4 [NAM(1)] (len=10, tl=0) 1,2,3,4,5,...
>  [1]  1  2  3  4  5  6  7  8  9 10
> @bdd6f80 14 REALSXP g0c6 [NAM(1)] (len=10, tl=0) 2,2,3,4,5,...
>  [1]  2  2  3  4  5  6  7  8  9 10
> @ba66278 14 REALSXP g0c6 [NAM(1)] (len=10, tl=0) 2,3,3,4,5,...
>  [1]  2  3  3  4  5  6  7  8  9 10
> @ba661e0 14 REALSXP g0c6 [NAM(1)] (len=10, tl=0) 2,3,4,4,5,...
>  [1]  2  3  4  4  5  6  7  8  9 10
> @ba65ee8 14 REALSXP g0c6 [NAM(1)] (len=10, tl=0) 2,3,4,5,5,...
>  [1]  2  3  4  5  5  6  7  8  9 10
> @ba65e50 14 REALSXP g0c6 [NAM(1)] (len=10, tl=0) 2,3,4,5,6,...
>  [1]  2  3  4  5  6  6  7  8  9 10
> @ba65db8 14 REALSXP g0c6 [NAM(1)] (len=10, tl=0) 2,3,4,5,6,...
>  [1]  2  3  4  5  6  7  7  8  9 10
> @ba65c88 14 REALSXP g0c6 [NAM(1)] (len=10, tl=0) 2,3,4,5,6,...
>  [1]  2  3  4  5  6  7  8  8  9 10
> @ba6a228 14 REALSXP g0c6 [NAM(1)] (len=10, tl=0) 2,3,4,5,6,...
>  [1]  2  3  4  5  6  7  8  9  9 10
> @ba6a190 14 REALSXP g0c6 [NAM(1)] (len=10, tl=0) 2,3,4,5,6,...
>  [1]  2  3  4  5  6  7  8  9 10 10
> @ba6a0f8 14 REALSXP g0c6 [NAM(1)] (len=10, tl=0) 2,3,4,5,6,...
>  [1]  2  3  4  5  6  7  8  9 10 11
>
> Notice that the memory reference is different each time. But according
> to http://r.789695.n4.nabble.com/full-copy-on-assignment-td1750555.html
> I (possibly a mistake on my part) understand that some optimization
> should be taking place.
>
> Is right to conclude from the output above that the entire vector is
> being copied each time or is just some kind of "shallow copy" (maybe
> some kind of view of the vector but not the vector itself is being
> copied). Obviously I'm not familiarized with r internals.
>
> Best regards
> --
> Carlos