如何在熊猫中对齐不同日期的时间序列？

import pandas as pd

df1 = pd.DataFrame({'date': ['2022-01-01', '2022-01-02', '2022-01-03'],
                    'value1': [1, 2, 3]})
df2 = pd.DataFrame({'date': ['2022-01-02', '2022-01-03', '2022-01-04'],
                    'value2': [4, 5, 6]})

df1['date'] = pd.to_datetime(df1['date'])
df2['date'] = pd.to_datetime(df2['date'])

merged_df = pd.merge(df1, df2, on='date', how='outer')

print(merged_df)

        date  value1  value2
0 2022-01-01     1.0     NaN
1 2022-01-02     2.0     4.0
2 2022-01-03     3.0     5.0
3 2022-01-04     NaN     6.0