Also something like ## generate zero-inflated Poisson data n <- 100 x1 <- rnorm(n) x2 <- rnorm(n) ind <- rbinom(n,1,1/(1+exp(-1-0.1*x1))) y <- ifelse(ind,rpois(n,lambda=exp(1+0.2*x2)),0)
There is at least zeroinfl in the CRAN package pscl and fmr in Lindsey's non-CRAN package gnlm for fitting zero-inflated regression models via maximum likelihood. > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of S Ellison > Sent: Wednesday, February 20, 2013 8:03 AM > To: lili puspita rahayu; r-help@R-project.org > Subject: Re: [R] generate variable y to produce excess zero in ZIP > analysis > > > Subject: [R] generate variable y to produce excess zero in > > ZIP analysis > > Maybe something like > > rzip <- function(n, lambda, zip=0.0) { > #zip is the desired proportion of _excess_ zeros > if(zip>1.0 || zip <0) stop("zip must be in (0,1)") > n.zip <- ceiling(zip*n) > n.pois <- n-n.zip > sample( c( rpois(n.pois, lambda), rep(0,n.zip) ) ) > } > > #Example > rzip(50, 3.5, zip=0.5) > > Having said that, I'd bet there's a package out there that already does > it better... > > S Ellison > > > > > > > > > Dear Mr/Mrs > > > > I am Lili Puspita Rahayu, student from magister third level > > of Statistics in Bogor Agriculture University. > > Mr/ > > Mrs, now I'm analyzing the Zero inflated Poisson (ZIP), which > > is a solution of the Poisson regression where the response > > variable (Y) has zero excess. ZIP now I was doing did not use > > real data, but using simulated data in R. Simulations by > > generating data on variables x1, x2, x3 with each size n = > > 100, after which generate data on response variable (Y). > > However, when I generate the variable y, after generating > > variables x1, x2, x3, then the simulation result in the > > variable y that does not have a zero excess. Sometimes just a > > coincidence there are 23%, 25% the proportion of zero on the > > variable Y. This is because I generate variables x1, x2, x3 > > with a distribution that has a small parameter values. I've > > been consulting with my lecturer, and suggested to generate > > variable Y that can control the proportion of zero on ZIP > > analysis. I've been trying to make the syntax, but has not > > succeeded.I would like to ask for assistance to R to make the > > syntax to generate simulated Y variables that can control the > > proportion of zeros after generating variables x1, x2, x3 on > > ZIP analysis.Thus, I can examine more deeply to determine how > > much the proportion of zeros on response variable (Y) that > > can be used in the Poisson regression analysis, parametric > > ZIP and ZIP semiparametric. > > > > syntax that I made previously by generating variable y > > without being controlled to produce zero excess in R : > > > > > b0=1.5 > > > b1=-log(2) > > > b2=log(3) > > > b3=log(4) > > > n=100 > > > x1<-rnorm(n, mean=5, sd=2) > > > x2<-runif(n, min=1, max=2) > > > x3<-rnorm(n, mean=10, sd=15) > > > > > > y<-seq(1,n) > > > for(i in 1:n) > > + { > > + m<-exp(b0+b1*x1[i]+b2*x2[i]+b3*x3[i]) > > + yp<-rpois(1,m) > > + y[i]<-yp > > + } > > > > > > I am very > > grateful for the assistance of R. > > I am looking forward to hearing from you. Thank you very much. > > > > Sincerely yours > > Lili Puspita Rahayu > > [[alternative HTML version deleted]] > > > > > > ******************************************************************* > This email and any attachments are confidential. Any use, copying or > disclosure other than by the intended recipient is unauthorised. If > you have received this message in error, please notify the sender > immediately via +44(0)20 8943 7000 or notify postmas...@lgcgroup.com > and delete this message and any copies from your computer and network. > LGC Limited. Registered in England 2991879. > Registered office: Queens Road, Teddington, Middlesex, TW11 0LY, UK > ______________________________________________ > 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.