Nanmdi, I think this is simply because a lot of time is taken transforming the matrix from logical (default when you create it) to numeric (when you add the number to [1,1]. If you do the same thing again to [1,2], it is done instantaneously: > a <- matrix(nrow=10000,ncol=10000) > system.time(a[1,1] <- 1903908.80385) user system elapsed 10.000 0.781 10.755 > > system.time(a[1,2] <- 1903908.80385) user system elapsed 0 0 0
By the way Rolf - I didn't see your full response last time through. I do know the difference between a matrix and a data.frame, thank you very much. On Fri, Apr 18, 2008 at 11:11 AM, Nnamdi <[EMAIL PROTECTED]> wrote: > > Still it is pretty slow when entering values into a large matrix. Case in > point: > > > a <- matrix(nrow=10000,ncol=10000) > > system.time(a[1,1] <- 1903908.80385) > user system elapsed > 30.840 6.226 41.416 > > is.matrix(a) > [1] TRUE > > Is there a better way to enter values into large matrices? If I have to > spend 41 secs each time I enter into a cell and I have 10000x10000 cells to > enter that is impractical! > > --Nnamdi > > > Rolf Turner-3 wrote: > > > > > > On 17/04/2008, at 9:33 AM, Charles C. Berry wrote: > > > > <snip> > > > >> I'll lay odds that Matthew's 'matrix' is actually a data.frame, and > >> I'll not be surprised if the columns are factors. > > > > <snip> > > > > I suspect that you're right. > > > > ***Why*** can't people distinguish between data frames and matrices? > > If they were the same <expletive deleted> thing, there wouldn't be two > > different terms for them, would there? > > > > cheers, > > > > Rolf Turner > > > > ###################################################################### > > > Attention:\ This e-mail message is privileged and confid...{{dropped:9}} > > > > ______________________________________________ > > 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. > > > > > > -- > View this message in context: > http://www.nabble.com/efficiently-replacing-values-in-a-matrix-tp16732795p16763578.html > Sent from the R help mailing list archive at Nabble.com. > > > > ______________________________________________ > 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. > -- Matthew C Keller Asst. Professor of Psychology University of Colorado at Boulder www.matthewckeller.com ______________________________________________ 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.