[R] How to Fit Inflated Negative Binomial

[Lorenzo Isella]

Dear All,
I am trying to fit some data both as a negative binomial and a zero 
inflated binomial.
For the first case, I have no particular problems, see the small snippet 
below

library(MASS) #a basic R library

set.seed(123) #to have reproducible results

x4 <- rnegbin(500, mu = 5, theta = 4)

#Now fit and check that we get the right parameters

fd <- fitdistr(x4, "Negative Binomial")

summary(fd)

#and mu and theta are as expected
#now I add artificially some zeros

x5 <- sample(c(x4,rep(0,100)))

However, when I artificially add some zeros (case of x5) I am unsure 
about how to proceed.
I found some material online

http://bit.ly/uPVzOT
http://bit.ly/rXnzKi

but I wonder if they are an overkill of what I am really after (a 
fitting a negative binomial with too many zeros).
Any suggestion is really appreciated.
Many thanks

Lorenzo