面板数据缺失值的填补如何进行？其中，stkcd表示公司证券代码，Accper表示年份，B001101000表示营业收入，但是有的公司年份数据缺失，缺失年份四年到一年不等，请问应该如何敲代码呢？谢谢各位啦


input str12 Stkcd float Accper double B001101000
"000008" 2016  1876006502.09
"000008" 2017  2330932161.16
"000008" 2018  2564901269.62
"000008" 2019  3220142984.66
"000008" 2020  1917519166.43
"000016" 2016 20299348136.21
"000016" 2017 31227763249.71
"000016" 2018 46126797341.33
"000016" 2019 55119125478.72
"000016" 2020 50351836554.87
"000017" 2016    141970520.8
"000017" 2017   137490597.69
"000017" 2018   119906950.34
"000017" 2019    76022687.75
"000017" 2020   117857480.17
"000020" 2016   619167770.74
"000020" 2017   858040132.74
"000020" 2018   637046707.03
"000020" 2019   721557440.51
"000020" 2020   691742269.12