Python/Pandas - KeyError 合并数据帧

Question

我有两个要合并的数据框:

target:

    version  city_id            code
id                                                                            
4         2        4   5736201000175   
26        2        3   8290265000183   
27        3        3   9529184000156   
30        3        3   9263064000150   
34        2        3   9312770000144   
54        1        3   8407830000140   
55        1        3   5590100000139   



city:

    federation_unit_id       name
id                                        
3                    8  SAO PAULO
4                    8   CAMPINAS
7                    8    BARUERI
8                    8  BEBEDOURO
9                    8     SANTOS

我想合并它们，将 target 的“city_id”与 city 的“id”合并，最终数据框如下所示:

target:

    version  city_id            code    federation_unit_id       name
id                                                                            
4         2        4   5736201000175                     8   CAMPINAS
26        2        3   8290265000183                     8  SAO PAULO
27        3        3   9529184000156                     8  SAO PAULO
30        3        3   9263064000150                     8  SAO PAULO
34        2        3   9312770000144                     8  SAO PAULO
54        1        3   8407830000140                     8  SAO PAULO
55        1        3   5590100000139                     8  SAO PAULO

为此，我尝试使用以下代码:

target=target.merge(city, left_on='city_id', right_on='id')

但是它一直让我收到以下 KeyError:

Traceback (most recent call last):
  File "/file.py", line 12, in <module>
target=target.merge(city, left_on='index', right_on='city_id')
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/core/frame.py", line 4437, in merge
copy=copy, indicator=indicator)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tools/merge.py", line 38, in merge
copy=copy, indicator=indicator)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tools/merge.py", line 210, in __init__
self.join_names) = self._get_merge_keys()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tools/merge.py", line 434, in _get_merge_keys
right_keys.append(right[rk]._values)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/core/frame.py", line 1997, in __getitem__
return self._getitem_column(key)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/core/frame.py", line 2004, in _getitem_column
return self._get_item_cache(key)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/core/generic.py", line 1350, in _get_item_cache
values = self._data.get(item)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/core/internals.py", line 3290, in get
loc = self.items.get_loc(item)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/indexes/base.py", line 1947, in get_loc
return self._engine.get_loc(self._maybe_cast_indexer(key))
  File "pandas/index.pyx", line 137, in pandas.index.IndexEngine.get_loc (pandas/index.c:4154)
  File "pandas/index.pyx", line 159, in pandas.index.IndexEngine.get_loc (pandas/index.c:4018)
  File "pandas/hashtable.pyx", line 675, in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:12368)
  File "pandas/hashtable.pyx", line 683, in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:12322)
KeyError: 'id'

我不知道我做错了什么:/有人可以帮忙吗？

Answer 1

您可以使用 join

target.join(city, on='city_id')

---

join 本质上是面向索引的。但是，您可以指定一个替代列以加入构成左侧的数据框中。如果我们在 target 上调用 join 方法，那么我们希望将 'city_id' 指定为该替代列。 city 数据框已经有了合适的索引。