inline below Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com
> -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On > Behalf > Of nqf > Sent: Monday, June 18, 2012 10:30 AM > To: r-help@r-project.org > Subject: [R] Trying to speed up an if/else statement in simulations > > Dear R-help, > > I am trying to write a function to simulate datasets of size n which contain > two time-to-event outcome variables with associated 'Event'/'Censored' > indicator variables (flag1 and flag2 respectively). One of these indicator > variables needs to be dependent on the other, so I am creating the first and > trying to use this to create the second using an if/else statement. > > My data structure needs to follow this algorithm (for each row of the data): > If flag1=1 then flag2 should be 1 with probability 0.95 and zero otherwise > Else if flag1=0 then flag2 should be 1 with probability 0.5 and zero > otherwise > > I can set up this example quite simply using if else statements, but this is > incredibly inefficient when running thousands of datasets: > data<-as.data.frame(rbinom(10,1,0.5)) > colnames(data)<-'flag1' > for (i in 1:n) { > if (data$flag1[i]==1) {data$flag2[i]<-rbinom(1,1,0.95)} else > {data$flag2[i]<-rbinom(1,1,0.5)} > } Do you mean n <- 10 data <- data.frame(flag1 = rbinom(n, 1, 0.5)) for(i in seq_len(n)) { if (data$flag1[i]==1) {data$flag2[i]<-rbinom(1,1,0.95)} else {data$flag2[i]<-rbinom(1,1,0.5)} } ? > > > I think to speed up the simulations I would be better changing to > vectorisation and using something like: > ifelse(data$flag1==1,rbinom(1,1,0.95),rbinom(1,1,0.5)) > but the rbinom statements here generate one value and repeat this draw for > every element of flag2 that matches the 'if' statement on flag1. Assuming that n is nrow(data), use data$flag2 <- ifelse(data$flag1==1, rbinom(n, 1, 0.95), rbinom(n, 1, 0.5)) so you get n independent draws from each distribution instead of 1. I prefer to factor out the common arguments as in data$flag2 <- rbinom(n, 1, ifelse(data$flag1==1, 0.95, 0.5)) > > Is there a way to assign flag2 to a new bernoulli draw for each subject in > the data frame with flag1=1? > > I hope my question is clear, and thank you in advance for your help. > > Thanks, > Natalie > PhD student, Reading University > > P.S. I am using R 2.12.1 on Windows 7. > > > -- > View this message in context: > http://r.789695.n4.nabble.com/Trying-to-speed-up-an-if- > else-statement-in-simulations-tp4633725.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.
