代码：
bys branch_name year:gen bank_branch_number=_N
bys year:gen bank_branch_number_city=_N
duplicates drop branch_name year bank_branch_number_city bank_branch_number,force
sort branch_name
drop branch_setup_date
sort year branch_name
bysort branch_name:gen branch_number=sum(bank_branch_number)
gen hhi=branch_number/bank_branch_number_city
gen HHI=hhi*hhi
问题：由于有些银行在某些年份没有建立新的网点，所以没有那些年份的数据，这样在计算HHI的时候，缺少数据年份的计算量就偏小，求大神帮忙解答如何插入一个数字循环，使得每个银行都有2009-2018的数据，新插入的数组有关数值赋值为0。