* created 7/93 : version 3.0                    ssa6: STB-22
program define firstocc
	version 3.0
	if "`1'"=="" {
		di "The syntax is: "
		di "firstocc <identifier_variable> <occurrence_variable> =exp [if] [in], gen(new_variable) sav(file_name)"
}
	local varlist "req ex min(2) max(3)"
	local if "opt"
	local in "opt"
	local exp "req nop"
	local options "GENerate(string) SAVing(string)"

	tempvar cum touse

	parse "`*'"
	parse "`varlist'", parse(" ")

	if "`varlist'"!="" { confirm var `varlist' }

	if _N==0 { err 2000 } 

	if "`generat'"=="" & "`saving'"=="" { 
		di in red "Options generate() or saving() must be specified"
		err 198
		}

	if "`generat'"!="" & "`saving'"!="" { 
		di in red "Only one option must be specified"
		err 198
		}

	if "`generat'"!="" {
		confirm new variable `generate'
	}

capture { 				/* Intercept break key	*/
	sort `1' `2' `3'

	by `1' : gen `touse'=1 `if' `in'
	by `1': gen int `cum'=sum(`exp')
	if "`generat'"=="" { 
		local generat "dummy"
		}
	by `1': gen byte `generat'=`cum'==1 & `cum'[_n-1]!=1 if `cum'!=. & `touse'==1
	if "`saving'"!="" { 
		keep if `generat'==1 
		drop `generat'
		noi save `saving'
		}
}
	local rc = _rc 
	error `rc'
end