On 12-May-11 09:02:45, Alexander Engelhardt wrote: > Am 12.05.2011 10:46, schrieb blutack: >> Hi, I need to create a function which generates a Binomial random >> number >> without using the rbinom function. Do I need to use the choose >> function or >> am I better just using a sample? >> Thanks. > > I think I remember other software who generates binomial data > with e.g. pi=0.7 by > > pi <- 0.7 > x <- runif(100)>pi > summary(x) > > -- Alex
That needs to be the other way round (and perhaps also convert it to 0/1): x <- 1*(runif(100) < pi) since Prob(runif > pi) = (1 - pi). Comparison: pi <- 0.7 x <- runif(100)>pi x[1:10] # [1] FALSE TRUE TRUE FALSE FALSE TRUE TRUE TRUE FALSE FALSE sum(x)/100 # [1] 0.36 x <- 1*(runif(100) < pi) x[1:10] # [1] 0 0 1 1 1 1 1 0 1 0 sum(x)/100 # [1] 0.62 Ted -------------------------------------------------------------------- E-Mail: (Ted Harding) <ted.hard...@wlandres.net> Fax-to-email: +44 (0)870 094 0861 Date: 12-May-11 Time: 10:21:26 ------------------------------ XFMail ------------------------------ ______________________________________________ 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.
