我的数据框看起来像这样:
JOINED_CO GENDER EXEC_FULLNAME GVKEY YEAR CONAME BECAMECEO REJOIN LEFTOFC LEFTCO RELEFT REASON PAGE CO_PER_ROL 5622 NaN MALE Ira A. Eichner 1004 1992 AAR CORP 19550101 NaN 19961001 19990531 NaN RESIGNED 79 5622 NaN MALE Ira A. Eichner 1004 1993 AAR CORP 19550101 NaN 19961001 19990531 NaN RESIGNED 79 5622 NaN MALE Ira A. Eichner 1004 1994 AAR CORP 19550101 NaN 19961001 19990531 NaN RESIGNED 79 5622 NaN MALE Ira A. Eichner 1004 1995 AAR CORP 19550101 NaN 19961001 19990531 …