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.
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.
