I don't see why making copies of the columns you need inside the loop is "better" memory management. If the data are in a matrix, accessing elements is quite fast. If you're worrying about speed of that, do what Charles suggest: work with the transpose so that you are accessing elements in the same column in each iteration of the loop.
Andy From: Federico Calboli > > Charles C. Berry wrote: > > > Whoa! You are accessing one ROW at a time. > > > > Either way this will tangle up your cache if you have many rows and > > columns in your orignal data. > > > > You might do better to do > > > > Y <- t( X ) ### use '<-' ! > > > > for (i in whatever ){ > > do something using Y[ , i ] > > } > > My question is NOT how to write the fastest code, it is > whether dummy variables (for lack of better words) make the > memory management better, i.e. faster, or not. > > Best, > > Fede > > -- > Federico C. F. Calboli > Department of Epidemiology and Public Health Imperial > College, St Mary's Campus Norfolk Place, London W2 1PG > > Tel +44 (0)20 7594 1602 Fax (+44) 020 7594 3193 > > f.calboli [.a.t] imperial.ac.uk > f.calboli [.a.t] gmail.com > > ______________________________________________ > R-help@stat.math.ethz.ch 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. > > > ------------------------------------------------------------------------------ Notice: This e-mail message, together with any attachments,...{{dropped}} ______________________________________________ R-help@stat.math.ethz.ch 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.