##for nested indexing--always works
#In STATA:


# Generate a new variable called newcode that counts from 1 to the number of groups(e.g. countries)

egen newcode = group(oldcode)

#generate time counter:
bysort newcode: gen time = _n
#########################################################
#
#NESTED INDEXING IN R:
##generate new group variable that is a sequence of integers starting ##with 1

uncode<-unique(dat$ccode)
for(i in 1:length(uncode))
dat$newcode[which(dat$ccode == uncode[i])]<-i

##generate a time counter:

dat<- dat[order(dat$newcode, dat$year) ,]
dat$time <- unlist(by(dat$year, list(dat$newcode), function(x) seq(1, length(x))))

dat<-dat[order(dat$time, dat$newcode),]

##write out dat with writeDatafileR:

writeDatafileR(dat, "c:/file.address.name.txt")

##DOUBLE LOOP FOR BALANCED PANELS ONLY!!!!
##transform variables into matrices--with correct dimensions.
##in this example there were 29 countries and 28 time points.

sepa<-matrix(dat$sepahost, nrow=29, ncol=28) 
sepal<-matrix(dat$sepahost, nrow=29, ncol=28)

##write file out using writeDatafileR and list

writeDatafileR(list(sepahost=sepa, sepalmho=sepal, N=29, J=28), "c:/structure.test.final.txt")