On Apr 14, 2008, at 4:22 PM, Stephen Milborrow wrote: >> Le sam. 12 avr. à 12:47, carlos martinez a écrit : >> Looking for a simple, effective a minimum execution time solution. >> >> For a vector as: >> >> c(0,0,1,0,1,1,1,0,0,1,1,0,1,0,1,1,1,1,1,1) >> >> To transform it to the following vector without using any loops: >> >> (0,0,1,0,1,2,3,0,0,1,2,0,1,0,1,2,3,4,5,6) > > Here is a fast solution using the Ra just-in-time compiler > www.milbo.users.sonic.net/ra. > > jit(1) > if (length(x) > 1) > for (i in 2:length(x)) > if (x[i]) > x[i] <- x[i-1] + 1 > > The times in seconds for various solutions mailed to r-devel are > listed > below. There is some variation between runs and with the contents of > x. The > times shown are for > > set.seed(1066); x <- as.double(runif(1e6) > .5) > > This was tested on a WinXP 3 GHz Pentium D with Ra 1.0.7 (based on R > 2.6.2). > The code to generate these results is attached. >
Well, if you want to break the rules, you may as well do it properly ;). library(inline) f = cfunction(signature(n="integer", x="numeric"), "for(int i = 1; i < *n; i++) if (x[i]) x[i] = x[i-1] + 1;", convention=".C") f(length(x), x) inline 0.03s pure 2.7s hadley 4.5s (I couldn't measure Ra reliably - I was getting times around 2s which seems inappropriate - Stephen, how did you measure it?). Cheers, S > vin 24 > greg 11 > had 3.9 > dan 1.4 > dan2 1.4 > jit 0.25 # code is shown above, 7 secs with standard R 2.6.2> > > Stephen Milborrow > www.milbo.users.sonic.net > <cm-post.R.txt>______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
