###########################
#  MAC fraility example -- R code to arrange the dataset
#    Weibull survival model -- Example 2.15
###########################


# Our dataset is unbalanced, as the number of subjects differs from site to site:
# nsub=c(4,2,1,10,8,12,6,6,13,4,3), i.e. there are 4 subjects in site 1, 2 in site 2, etc.
#
# We use "offset" to hold the position in the dataset at which each person's data starts. 
# Here is a snippet of R code to calculate offset from nsub:

    nsub<-c(4,2,1,10,8,12,6,6,13,4,3)
    temp<-1
    offset<-rep(0,(length(nsub)+1))
    for(i in 1:length(nsub)){offset[i]<-temp; temp<-temp+nsub[i]}
    offset[ (length(nsub)+1)] <-sum(nsub)+1