Dear Michael,
thank you for the enlightenment. Just for the records, here is the
solution that Michael referred to:
http://developer.r-project.org/Refcnt.html
Best,
Denes
On 06/03/2014 03:57 PM, Michael Lawrence wrote:
This is because R keeps track of the names of an object, until there are
2 names. Thus, once it reaches 2, it can no longer decrement the named
count. In this example, 'a' reaches 2 names ('a' and 'b'), thus R does
not know that 'a' only has one name at the end.
Luke has added reference counting to R 3.1 to get around these types of
problems. If you want to try it out, make the necessary change in
Rinternals.h and recompile. With reference counting, R knows that 'a'
only has one reference and avoids the copy.
> a <- seq.int <http://seq.int>(10)
> a[1:4] <- 4:1
> b <- a
> .Internal(inspect(a))
@2b71608 13 INTSXP g0c4 [REF(2)] (len=10, tl=0) 4,3,2,1,5,...
> b[1:4] <- 1:4
> .Internal(inspect(b))
@2b715a0 13 INTSXP g0c4 [REF(1)] (len=10, tl=0) 1,2,3,4,5,...
> .Internal(inspect(a))
@2b71608 13 INTSXP g0c4 [REF(1)] (len=10, tl=0) 4,3,2,1,5,...
> a[1:4] <- 1:4
> .Internal(inspect(a))
@2b71608 13 INTSXP g0c4 [REF(1)] (len=10, tl=0) 1,2,3,4,5,...
On Mon, Jun 2, 2014 at 9:31 AM, Dénes Tóth <toth.de...@ttk.mta.hu
<mailto:toth.de...@ttk.mta.hu>> wrote:
Hi,
Please consider the following code:
a <- seq.int <http://seq.int>(10) # create a
tracemem(a)
a[1:4] <- 4:1 # no internal copy
b <- a # no internal copy
b[1:4] <- 1:4 # copy, b is not a any more
a[1:4] <- 1:4 # copy, but why?
With results:
> a <- seq.int <http://seq.int>(10)
> tracemem(a)
[1] "<0x1792bc0>"
> a[1:4] <- 4:1
> b <- a
> b[1:4] <- 1:4
tracemem[0x1792bc0 -> 0x1792b58]:
> a[1:4] <- 1:4
tracemem[0x1792bc0 -> 0x1792af0]:
##
Could you provide a brief explanation or point me to a source why R
needs a copy in the final step?
Best,
Denes
> sessionInfo()
R version 3.1.0 (2014-04-10)
Platform: x86_64-pc-linux-gnu (64-bit)
locale:
[1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
[3] LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
[5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8
[7] LC_PAPER=en_US.UTF-8 LC_NAME=C
[9] LC_ADDRESS=C LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics grDevices utils datasets methods base
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