pandas pd.merge_ordered() 按排序（时序）合并

pandas.merge_ordered(
    left, 
    right, 
    on=None, 
    left_on=None, 
    right_on=None, 
    left_by=None, 
    right_by=None, 
    fill_method=None, 
    suffixes=('_x', '_y'), 
    how='outer'
)

from pandas import merge_ordered
df1 = pd.DataFrame(
    {
        "key": ["a", "c", "e", "a", "c", "e"],
        "lvalue": [1, 2, 3, 1, 2, 3],
        "group": ["a", "a", "a", "b", "b", "b"]
    }
)
df1
'''
  key  lvalue group
0   a       1     a
1   c       2     a
2   e       3     a
3   a       1     b
4   c       2     b
5   e       3     b
'''

df2 = pd.DataFrame({"key": ["b", "c", "d"], "rvalue": [1, 2, 3]})
df2
'''
  key  rvalue
0   b       1
1   c       2
2   d       3
'''

merge_ordered(df1, df2, fill_method="ffill", left_by="group")
'''
  key  lvalue group  rvalue
0   a       1     a     NaN
1   b       1     a     1.0
2   c       2     a     2.0
3   d       2     a     3.0
4   e       3     a     3.0
5   a       1     b     NaN
6   b       1     b     1.0
7   c       2     b     2.0
8   d       2     b     3.0
9   e       3     b     3.0
'''

import pandas as pd

# 构造示例数据
data1 = pd.DataFrame({
    'date': ['2021-01-01', '2021-01-02', '2021-01-03'],
    'value1': [1, 2, 3]
})

data2 = pd.DataFrame({
    'date': ['2021-01-02', '2021-01-03', '2021-01-04'],
    'value2': [10, 20, 30]
})

print("data1:")
print(data1)

print("\ndata2:")
print(data2)

# 使用 merge_ordered 合并数据
merged_data = pd.merge_ordered(data1, data2, on='date', fill_method='ffill')

print("\n合并后的数据:")
print(merged_data)

data1:
         date  value1
0  2021-01-01       1
1  2021-01-02       2
2  2021-01-03       3

data2:
         date  value2
0  2021-01-02      10
1  2021-01-03      20
2  2021-01-04      30

合并后的数据:
         date  value1  value2
0  2021-01-01     1.0     NaN
1  2021-01-02     2.0    10.0
2  2021-01-03     3.0    20.0
3  2021-01-04     3.0    30.0