Pandas -2数据帧，将df1的索引列添加到第二列上的df2

Question

我有两个数据帧：

df1 (sample, has more columns):

+---+----------------+--------------+-----------+
|   |     Region     | Placement ID |   Units   |
+---+----------------+--------------+-----------+
| 0 | Western Europe | 1.10872E+13  | 367628.76 |
| 1 | Western Europe | 1.10872E+13  | 367628.76 |
| 2 | Western Europe | 1.10872E+13  | 74604.63  |
+---+----------------+--------------+-----------+

df2 (sample, has more columns:

+-----------+----------------+--------------+
| Creatives | Publisher Name | Placement ID |
+-----------+----------------+--------------+
| Temenos   | Quantcast      | 1.10872E+13  |
| Temenos   | Quantcast      | 1.10872E+13  |
| Temenos   | Quantcast      | 1.10872E+13  |
+-----------+----------------+--------------+

我想做的是根据Placement ID在dataframe 2中添加一个额外的列，其中包含dataframe 1的索引列。

数据框1或2中的某些放置Id字段可能为空，或具有错误的值。如果不匹配或发现错误，则我想添加一个缺少或错误的值，如N/A、Missing或留空

Answer 1

IIUC您需要merge，但存在重复项的问题，因此首先使用drop_duplicates删除它们，然后选择一列用于添加，另一列用于join (Placement ID)：

print (pd.merge(df2, 
                df1.drop_duplicates('Placement ID')[['Units', 'Placement ID']], 
                how='left', 
                on='Placement ID'))


  Creatives Publisher Name  Placement ID      Units
0   Temenos      Quantcast  1.108720e+13  367628.76
1   Temenos      Quantcast  1.108720e+13  367628.76
2   Temenos      Quantcast  1.108720e+13  367628.76

如果需要添加索引，则需要reset_index

print (pd.merge(df2, 
                df1.drop_duplicates('Placement ID')
                   .reset_index()[['level_0','Placement ID']], 
                how='left', 
                on='Placement ID'))
  Creatives Publisher Name  Placement ID  level_0
0   Temenos      Quantcast  1.108720e+13        0
1   Temenos      Quantcast  1.108720e+13        0
2   Temenos      Quantcast  1.108720e+13        0

需要删除重复项，因为通过连接键merge多行-在df2中有3个相同的值1.108720e+13，在df1中有3行，因此获得3x3行，如下所示：

print (pd.merge(df2, 
                df1.reset_index()[['level_0', 'Placement ID']], 
                how='left', 
                on='Placement ID'))

  Creatives Publisher Name  Placement ID  level_0
0   Temenos      Quantcast  1.108720e+13        0
1   Temenos      Quantcast  1.108720e+13        1
2   Temenos      Quantcast  1.108720e+13        2
3   Temenos      Quantcast  1.108720e+13        0
4   Temenos      Quantcast  1.108720e+13        1
5   Temenos      Quantcast  1.108720e+13        2
6   Temenos      Quantcast  1.108720e+13        0
7   Temenos      Quantcast  1.108720e+13        1
8   Temenos      Quantcast  1.108720e+13        2