So you want to generate random multinomials ? ... Just generate random uniforms and divide by their sum!
z <- runif(3); z/sum(z) ## This can easily be modified to generate lots of random multinomial 3 vectors, e.g. z <- matrix( runif(3*100), ncol=3) z/rowSums(z) ## each row is a random multinomial -- Bert On Tue, Mar 29, 2011 at 9:34 AM, Petr Savicky <savi...@praha1.ff.cuni.cz> wrote: > On Tue, Mar 29, 2011 at 11:20:13AM -0500, Christopher Desjardins wrote: >> I have 3 vectors: p1, p2, and p3. I would like each vector to be any >> possible value between 0 and 1 and p1 + p2 + p3 = 1. I want to graph these >> and I've thought about using scatterplot3d(). Here's what I have so far. >> >> library(scatterplot3d) >> p1 <- c(1,0,0,.5,.5,0,.5,.25,.25,.34,.33,.33,.8,.1,.1,.9,.05,.05) >> p2 <- c(0,1,0,.5,0,.5,.25,.5,.25,.33,.34,.33,.1,.8,.1,.05,.9,.05) >> p3 <- c(0,0,1,0,.5,.5,.25,.25,.5,.33,.33,.34,.1,.1,.8,.05,.05,.9) >> scatterplot3d(p1,p2,p3) >> >> >> However, I wonder if there is an easy way to create vectors p1, p2, and p3. > > Hi. > > The vectors p1, p2 and p3 are not uniquely determined. Try, for example, > the following > > n <- 16 > pp <- expand.grid(p1=0:n, p2=0:n, p3=0:n) > pp <- subset(pp, p1 + p2 + p3 == n) > p1 <- pp$p1/n > p2 <- pp$p2/n > p3 <- pp$p3/n > > If n is a power of 2, then p1 + p2 + p3 will be exactly all ones vector. > Otherwise, there may be differences within machine rounding error. > > Hope this helps. > > Petr Savicky. > > ______________________________________________ > 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. > -- Bert Gunter Genentech Nonclinical Biostatistics 467-7374 http://devo.gene.com/groups/devo/depts/ncb/home.shtml ______________________________________________ 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.
