将细分的行业industry作为虚拟变量i.industry进行回归,怎么做?数据如下
tkcd year industry
8 2015 "C37"
8 2016 "C37"
8 2017 "C37"
8 2018 "C37"
8 2019 "C37"
12 2015 "C30"
12 2017 "C30"
12 2018 "C30"
12 2019 "C30"
12 2020 "C30"
16 2017 "C39"
16 2018 "C39"
16 2019 "C39"
19 2016 "A15"