我有一个通过df.pivot创建的数据框:typestartendF_Typeto_dateA20150908143000345316B20150908140300NaN48020150908140600NaN12020150908143000107438803C20150908140100NaN171520150908140200NaN106220150908141000NaN14520150908141500418NaN20150908141800NaN4502015090814290019731499201509081430001952216659D201509081430004