*首先将date中的“-”去掉
replace date=subinstr(date,"-","",.)
*然后分离年份和日期
gen year=substr(date,1,4)
gen md= substr(date,5,4)
destring year,replace force
destring md,replace force
egen A=group(stcode md)
xtset A year
gen cp_lag=L.cp
*首先将date中的“-”去掉
replace date=subinstr(date,"-","",.)
*然后分离年份和日期
gen year=substr(date,1,4)
gen md= substr(date,5,4)
destring year,replace force
destring md,replace force
egen A=group(stcode md)
xtset A year
gen cp_lag=L.cp