📅  最后修改于: 2022-03-11 14:46:05.277000             🧑  作者: Mango
df['day'] = df['day'].map(lambda x: pd.datetime(x.year, x.month, 1))
print (df)
day
0 2016-07-01
1 2016-08-01
2 2016-09-01
3 2016-10-01
4 2016-11-01