Oops, my version added cc instead of subtracted, it still works if you multiply cc by -1 (except the initial 1).
-- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- > project.org] On Behalf Of Greg Snow > Sent: Monday, November 08, 2010 1:15 PM > To: PLucas; r-help@r-project.org > Subject: Re: [R] How to eliminate this for loop ? > > If you are willing to shift the c vector by 1 and have 1 (the initial > value) as the start of c, then you can just do: > > cumsum( cc * b^( (n-1):0 ) ) / b^( (n-1):0 ) > > to compare: > > cc <- c(1, rnorm(999) ) > b <- 0.5 > n <- length(cc) > > a1 <- numeric(100) > a1[1] <- 1 > > system.time(for(i in 2:n ) { > a1[i] <- b*a1[i-1] + cc[i] > }) > > system.time(a2 <- cumsum( cc * b^( (n-1):0 ) ) / b^( (n-1):0 )) > > all.equal(a1,a2) > > Though you could have problems with the b^ part if the length gets too > long. > > -- > Gregory (Greg) L. Snow Ph.D. > Statistical Data Center > Intermountain Healthcare > greg.s...@imail.org > 801.408.8111 > > > > -----Original Message----- > > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- > > project.org] On Behalf Of PLucas > > Sent: Monday, November 08, 2010 2:26 AM > > To: r-help@r-project.org > > Subject: [R] How to eliminate this for loop ? > > > > > > Hi, I would like to create a list recursively and eliminate my for > loop > > : > > > > a<-c() > > a[1] <- 1; # initial value > > for(i in 2:N) { > > a[i]<-a[i-1]*b - c[i-1] # b is a value, c is another vector > > } > > > > > > Is it possible ? > > > > Thanks > > -- > > View this message in context: http://r.789695.n4.nabble.com/How-to- > > eliminate-this-for-loop-tp3031667p3031667.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. > > ______________________________________________ > 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. ______________________________________________ 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.
