python panda在两个轴上连接数据帧（在所有方向合并）

Question

抱歉，如果这是一个重复，我不知道相关的关键字，我面临的问题。我正在阅读一系列的数据帧，并尝试将每个数据帧连接到一个单独的大数据帧中。dfs是时间序列数据，有些需要垂直追加，有些需要水平追加。有几千个，但是这个例子抓住了这个问题。在

问题是，我找不到一个pandas函数，它可以处理两个方向的合并，而不需要事先知道读入的内容。在

import pandas as pd


df1 = pd.DataFrame({'GMT_date': ["01-01-2000","02-01-2000","03-01-2000","04-01-2000","05-01-2000"] ,
                   'LOWI_Precipitation_24_Hour_(mm)': [2.2, 0, 0.2, 0.4, 0]})

df2 = pd.DataFrame({'GMT_date': ["06-01-2000","07-01-2000","08-01-2000","09-01-2000","10-01-2000"] ,
                   'LOWI_Precipitation_24_Hour_(mm)': [0.1, 0.1, 3.1, 4.0, 0]})

df3 = pd.DataFrame({'GMT_date': ["06-01-2000","07-01-2000","08-01-2000","09-01-2000","10-01-2000"] ,
                   'TGPY_Precipitation_24_Hour_(mm)': [0.6, 0.7, 5.1, 1.0, 2.0]})  

df_list = [df1, df2, df3]

merged_df = pd.DataFrame()

for df in df_list:
    merged_df = merged_df.merge(df, how='outer', left_index=True, right_index=True)
print(merged_df)

GMT_date_x  LOWI_Precipitation_24_Hour_(mm)_x  GMT_date_y  LOWI_Precipitation_24_Hour_(mm)_y    GMT_date  TGPY_Precipitation_24_Hour_(mm)
0  01-01-2000                                2.2  06-01-2000                                0.1  06-01-2000                              0.6
1  02-01-2000                                0.0  07-01-2000                                0.1  07-01-2000                              0.7
2  03-01-2000                                0.2  08-01-2000                                3.1  08-01-2000                              5.1
3  04-01-2000                                0.4  09-01-2000                                4.0  09-01-2000                              1.0
4  05-01-2000                                0.0  10-01-2000                                0.0  10-01-2000                              2.0

如您所见，这些列已为每个df分配了一个新列，我希望它们在一个列中。我还尝试了以下合并：

^{pr2}$

产生：

     GMT_date  LOWI_Precipitation_24_Hour_(mm)  TGPY_Precipitation_24_Hour_(mm)
0  01-01-2000                              2.2                              NaN
1  02-01-2000                              0.0                              NaN
2  03-01-2000                              0.2                              NaN
3  04-01-2000                              0.4                              NaN
4  05-01-2000                              0.0                              NaN
0  06-01-2000                              0.1                              NaN
1  07-01-2000                              0.1                              NaN
2  08-01-2000                              3.1                              NaN
3  09-01-2000                              4.0                              NaN
4  10-01-2000                              0.0                              NaN
0  06-01-2000                              NaN                              0.6
1  07-01-2000                              NaN                              0.7
2  08-01-2000                              NaN                              5.1
3  09-01-2000                              NaN                              1.0
4  10-01-2000                              NaN                              2.0

现在日期在我想要的一列中，但是日期列中有重复的。我试过了：

merged_df = merged_df.join(df)

这会引发一个错误：

ValueError: columns overlap but no suffix specified: Index(['GMT_date', 'LOWI_Precipitation_24_Hour_(mm)'], dtype='object')

我还尝试过将索引设置为GMT\U日期：

for df in df_list:
    df = df.set_index('GMT_date')
    merged_df = pd.concat([merged_df, df], axis=1)
print(merged_df)

            LOWI_Precipitation_24_Hour_(mm)  LOWI_Precipitation_24_Hour_(mm)  TGPY_Precipitation_24_Hour_(mm)
01-01-2000                              2.2                              NaN                              NaN
02-01-2000                              0.0                              NaN                              NaN
03-01-2000                              0.2                              NaN                              NaN
04-01-2000                              0.4                              NaN                              NaN
05-01-2000                              0.0                              NaN                              NaN
06-01-2000                              NaN                              0.1                              0.6
07-01-2000                              NaN                              0.1                              0.7
08-01-2000                              NaN                              3.1                              5.1
09-01-2000                              NaN                              4.0                              1.0
10-01-2000                              NaN                              0.0                              2.0

这会将日期解析为一列，并且没有重复的日期，但是现在我将数据分散到两列同名的列中？在

我一定缺少一个简单的函数或参数，它可以在一行中解决两个方向的合并问题？在

我试着看看：pd.合并但它似乎只返回两个df共享的日期。在

我希望有一个简单的解决办法？感觉好像不是'how'：{'left'、'right'、'outer'、'inner'}我需要一个merge中的'all'选项。在

Answer 1

我有另一个解决方案，在连接所有数据帧后，使用groupby合并重复列

import pandas as pd
import numpy as np
df1 = pd.DataFrame({'GMT_date': ["01-01-2000", "02-01-2000", "03-01-2000", "04-01-2000", "05-01-2000"],
                    'LOWI_Precipitation_24_Hour_(mm)': [2.2, 0, 0.2, 0.4, 0]})

df2 = pd.DataFrame({'GMT_date': ["06-01-2000", "07-01-2000", "08-01-2000", "09-01-2000", "10-01-2000"],
                    'LOWI_Precipitation_24_Hour_(mm)': [0.1, 0.1, 3.1, 4.0, 0]})

df3 = pd.DataFrame({'GMT_date': ["06-01-2000", "07-01-2000", "08-01-2000", "09-01-2000", "10-01-2000"],
                    'TGPY_Precipitation_24_Hour_(mm)': [0.6, 0.7, 5.1, 1.0, 2.0]})

df_list = [df1, df2, df3]
merged_df = pd.DataFrame()

for df in df_list:
    df = df.set_index('GMT_date')

    merged_df = pd.concat([merged_df, df], axis=1)

merged_df = merged_df.groupby(level=0, axis=1).agg(np.max)

print(merged_df)

输出：

^{pr2}$

---

你可以用

merged_df = merged_df.groupby(level=0, axis=1).agg(np.max if np.nan else sum) # if there is `Nan` then it will take `np.max` else take sum of values