On 04/04/2010 05:27 PM, Norm Matloff wrote: > Thanks very much. > > By the way, I tried setting a GDB breakpoint at duplicate1(), with the > following: > > > x <- 1:10000000 > > x[3] <- 8 > > x[33] <- 88
Here's how I investigated this, with the last line somewhat surprising R -d gdb gdb> r ... cntrl-C gdb> break duplicate1 gdb> commands > call Rf_PrintValue(s) > c > end gdb> c then x=5:1 x[1L] = 1L # no copy x[1L] = 10 # type coercion, new alloc but no copy x[1] = 20 # copy of index (!) Martin > > I found that duplicate1() was called on both of the latter two lines. > I was a bit surprised, since change-on-write would seem to imply that > copying would be done in that second line but NOT on the third. > Moreover, system.time() gave 0.284 user time for the second and 0 on > the third. YET duplicate1() WAS called on the third, and in stepping > through the code, there didn't seem to be an immediate exit. > > Thanks to both John and Duncan for their comment on the fact that using > [<- directly is a very different situation. That's not what I asked, > but the comment is useful to me for other reasons. > > Norm > >> Message: 4 >> Date: Sat, 03 Apr 2010 17:54:58 -0700 >> From: John Chambers <j...@r-project.org> >> To: r-devel@r-project.org >> Subject: Re: [Rd] full copy on assignment? > ... > ... >> How often does y get duplicated? Hopefully not a million times. One can >> look at this in gdb, by trapping calls to duplicate1. The answer is: >> just once, to ensure that the object is local. Then the duplicated >> version has only one reference and the primitive replacement doesn't >> copy it. > ... > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel -- Martin Morgan Computational Biology / Fred Hutchinson Cancer Research Center 1100 Fairview Ave. N. PO Box 19024 Seattle, WA 98109 Location: Arnold Building M1 B861 Phone: (206) 667-2793 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
