On Mon, 30 Nov 2020, Duncan Murdoch wrote:
On 30/11/2020 5:12 a.m., Georg Kindermann wrote:
Dear list members,
I was wondering why R is making a copy-on-modification after using str.
This isn't really an explanation, but adds a bit more data. If you inspect m
before and after str(), you'll see that str(m) leaves it with two references:
m <- matrix(1:12, 3)
.Internal(inspect(m))
@7fcb0ad682c8 13 INTSXP g0c4 [REF(1),ATT] (len=12, tl=0) 1,2,3,4,5,...
ATTRIB:
@7fcaf5f7b8a0 02 LISTSXP g0c0 [REF(1)]
TAG: @7fcafd091a80 01 SYMSXP g1c0 [MARK,REF(65535),LCK,gp=0x6000] "dim"
(has value)
@7fcb0afecc80 13 INTSXP g0c1 [REF(65535)] (len=2, tl=0) 3,4
str(m)
int [1:3, 1:4] 1 2 3 4 5 6 7 8 9 10 ...
.Internal(inspect(m))
@7fcb0ad682c8 13 INTSXP g0c4 [REF(2),ATT] (len=12, tl=0) 1,2,3,4,5,...
ATTRIB:
@7fcaf5f7b8a0 02 LISTSXP g0c0 [REF(1)]
TAG: @7fcafd091a80 01 SYMSXP g1c0 [MARK,REF(65535),LCK,gp=0x6000] "dim"
(has value)
@7fcb0afecc80 13 INTSXP g0c1 [REF(65535)] (len=2, tl=0) 3,4
It's not just str(): this sequence also does it.
m <- matrix(1:12, 3)
debug(mean)
mean(m)
This is due to the restarts needed by do_browser() creating links to
the environment that could be cleaned up in endcontext. There is a
runtime cost to doing so, but probably worth looking into.
Best,
luke
Hit c a couple of times now to get out of debugging, and m is left with two
references to it. I don't see that if mean isn't being debugged.
Duncan Murdoch
m <- matrix(1:12, 3)
tracemem(m)
#[1] "<0x559df861af28>"
dim(m) <- 4:3
m[1,1] <- 0L
m[] <- 12:1
str(m)
# int [1:4, 1:3] 12 11 10 9 8 7 6 5 4 3 ...
dim(m) <- 3:4 #Here after str a copy is made
#tracemem[0x559df861af28 -> 0x559df838e4a8]:
dim(m) <- 3:4
str(m)
# int [1:3, 1:4] 12 11 10 9 8 7 6 5 4 3 ...
dim(m) <- 3:4 #Here again after str a copy
#tracemem[0x559df838e4a8 -> 0x559df82c9d78]:
Also I was wondering why a copy is made when having a Task Callback.
TCB <- addTaskCallback(function(...) TRUE)
m <- matrix(1:12, nrow = 3)
tracemem(m)
#[1] "<0x559dfa79def8>"
dim(m) <- 4:3 #Copy on modification
#tracemem[0x559dfa79def8 -> 0x559dfa8998e8]:
removeTaskCallback(TCB)
#[1] TRUE
dim(m) <- 4:3 #No copy
I am using R version 4.0.3.
Kind regards,
Georg
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______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa Phone: 319-335-3386
Department of Statistics and Fax: 319-335-3017
Actuarial Science
241 Schaeffer Hall email: luke-tier...@uiowa.edu
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
______________________________________________
R-help@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.
