python - 连接 pandas DataFrames 只保留列中具有匹配值的行？

Question

我正在尝试“合并连接”两个 pandas DataFrame。基本上，我想堆叠两个 DataFrame，但只保留每个 DataFrame 中与另一个 DataFrame 中的值匹配的行。例如:

data1:

+---+------------+-----------+-------+
|   | first_name | last_name | class |
+---+------------+-----------+-------+
| 0 | Alex       | Anderson  |     1 |
| 1 | Amy        | Ackerman  |     2 |
| 2 | Allen      | Ali       |     3 |
| 3 | Alice      | Aoni      |     4 |
| 4 | Andrew     | Andrews   |     4 |
| 5 | Ayoung     | Atiches   |     5 |
+---+------------+-----------+-------+

data2:

+---+------------+-----------+-------+
|   | first_name | last_name | class |
+---+------------+-----------+-------+
| 0 | Billy      | Bonder    |     4 |
| 1 | Brian      | Black     |     5 |
| 2 | Bran       | Balwner   |     6 |
| 3 | Bryce      | Brice     |     7 |
| 4 | Betty      | Btisan    |     8 |
| 5 | Bruce      | Bronson   |     8 |
+---+------------+-----------+-------+

然后在 data1 和 data2 上执行此操作后生成的数据帧应如下所示:

result:

+---+------------+-----------+-------+
|   | first_name | last_name | class |
+---+------------+-----------+-------+
| 3 | Alice      | Aoni      |     4 |
| 4 | Andrew     | Andrews   |     4 |
| 5 | Ayoung     | Atiches   |     5 |
| 0 | Billy      | Bonder    |     4 |
| 1 | Brian      | Black     |     5 |
+---+------------+-----------+-------+

基本上，我试图合并两个数据集，然后堆叠列。我可以想出几种方法来做到这一点，但它们都是 hack-y。我可以合并 data1 和 data2 然后堆叠列，或者使用像这样的 map :

map1 = data1['subject_id'].map(lambda x: x in list(data2['subject_id']))
map2 = data2['subject_id'].map(lambda x: x in list(data1['subject_id']))
pd.concat([data1[map1], data2[map2]])

但是有没有更优雅的解决方案呢？

Answer 1

这个怎么样？

In [335]: cls = np.intersect1d(data1['class'], data2['class'])

In [336]: cls
Out[336]: array([4, 5], dtype=int64)

In [337]: pd.concat([data1.ix[data1['class'].isin(cls)], data2.ix[data2['class'].isin(cls)]])
Out[337]:
  first_name last_name  class
3      Alice      Aoni      4
4     Andrew   Andrews      4
5     Ayoung   Atiches      5
0      Billy    Bonder      4
1      Brian     Black      5

或:

In [338]: data1.ix[data1['class'].isin(cls)].append(data2.ix[data2['class'].isin(cls)])
Out[338]:
  first_name last_name  class
3      Alice      Aoni      4
4     Andrew   Andrews      4
5     Ayoung   Atiches      5
0      Billy    Bonder      4
1      Brian     Black      5