On Aug 16, 2013, at 2:23 PM, Gang Peng wrote: > If you don't want to copy the data, you can use environments. You can first > define x and y in the global environment and then in the function, use > function get() to get x, y in the global environment. When you change x and > y in the function, x and y also change in the global environment. >
That doesn't sound like the behavior I expect in R. Do you care to illustrate this? -- David. > Best, > Gang > > > 2013/8/16 MRipley <mrip...@gmail.com> > >> Usually R is pretty good about not copying objects when it doesn't need >> to. However, the list() function seems to make unnecessary copies. For >> example: >> >>> system.time(x<-double(10^9)) >> user system elapsed >> 1.772 4.280 7.017 >>> system.time(y<-double(10^9)) >> user system elapsed >> 2.564 3.368 5.943 >>> system.time(z<-list(x,y)) >> user system elapsed >> 5.520 6.748 12.304 >> >> I have a function where I create two large arrays, manipulate them in >> certain ways, and then return both as a list. I'm optimizing the function, >> so I'd like to be able to build the return list quickly. The two large >> arrays drop out of scope immediately after I make the list and return it, >> so copying them is completely unnecessary. >> >> Is there some way to do this? I'm not familiar with manipulating lists >> through the .Call interface, and haven't been able to find much about this >> in the documentation. Might it be possible to write a fast (but possibly >> unsafe) list function using .Call that doesn't make copies of the arguments? >> >> PS A few things I've tried. First, this is not due to triggering garbage >> collection -- even if I call gc() before list(x,y), it still takes a long >> time. >> >> Also, I've tried rewriting the function by creating the list at the >> beginning as in: >> result <- list(x=double(10^9),y=double(**10^9)) >> and then manipulating result$x and result$y but this made my code run >> slower, as R seemed to be making other unnecessary copies while >> manipulating elements of a list like this. >> >> I've considered (though not implemented) creating an environment rather >> than a list, and returning the environment, but I'd rather find a simple >> way of creating a list without making copies if possible. >> >> ______________________________**________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/**listinfo/r-help<https://stat.ethz.ch/mailman/listinfo/r-help> >> PLEASE do read the posting guide http://www.R-project.org/** >> posting-guide.html <http://www.R-project.org/posting-guide.html> >> and provide commented, minimal, self-contained, reproducible code. >> > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list > 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. David Winsemius Alameda, CA, USA ______________________________________________ R-help@r-project.org mailing list 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.
