clear
cd e:\chililabdata\data
use inmigration
replace img_date=img_date/86400000
format img_date %td
gen year = year( img_date)
drop if year < 2004
gen h = halfyear(img_date)
gen round = yh(year,h)-89
drop  if round > 19
tostring round, generate(rounds)
replace rounds = "0" + rounds if strlen(rounds) ==1
gen socialkey = socialgpid+  rounds
gen individkey = individid+  rounds
drop  EID h socialgpidGuid rounds  eventid observeid year
duplicates drop individkey, force
drop if round < 0
save rImmigration, replace