gen date_trade=date(date, "YMD")
gen date_ann=date(date_announce, "YMD")
by code: gen dum_date_announce=0 if date_ann>date_trade[_n-1] & date_ann<=date_trade
replace dum_date_announce=1 if dum_date_announce!=0
replace code_dum=code_dum[_n-1] if code==code[_n-1]
keep if code_dum==. // nontradingnum>5 & dum_date_announce==0
drop code_dum