0
我試圖將下面的代碼確定的列的累積最大
df = pd.DataFrame([[23, 52], [36, 49], [52, 61], [75, 82], [97, 12]], columns=['A', 'B'])
df['C'] = np.where(df['A'] > df['C'].shift(), df['A'], df['C'].shift())
print(df)
假設是第一df['C].shift()操作應假定爲0（由於df['C']是不存在的）
預期輸出
A B C
0 23 52 23
1 36 49 36
2 12 61 36
3 75 82 75
4 70 12 75
但我得到一個KeyError異常。
Traceback (most recent call last):
File "C:\Program Files\Python36\lib\site-packages\pandas\core\indexes\base.py", line 2442, in get_loc
return self._engine.get_loc(key)
File "pandas\_libs\index.pyx", line 132, in pandas._libs.index.IndexEngine.get_loc (pandas\_libs\index.c:5280)
File "pandas\_libs\index.pyx", line 154, in pandas._libs.index.IndexEngine.get_loc (pandas\_libs\index.c:5126)
File "pandas\_libs\hashtable_class_helper.pxi", line 1210, in pandas._libs.hashtable.PyObjectHashTable.get_item (pandas\_libs\hashtable.c:20523)
File "pandas\_libs\hashtable_class_helper.pxi", line 1218, in pandas._libs.hashtable.PyObjectHashTable.get_item (pandas\_libs\hashtable.c:20477)
KeyError: 'C'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "C:\Users\Development\workspace\TestPython\TestPython.py", line 6, in <module>
df['C'] = np.where(df['A'] > df['C'].shift(), df['B'].shift(), df['A'])
File "C:\Program Files\Python36\lib\site-packages\pandas\core\frame.py", line 1964, in __getitem__
return self._getitem_column(key)
File "C:\Program Files\Python36\lib\site-packages\pandas\core\frame.py", line 1971, in _getitem_column
return self._get_item_cache(key)
File "C:\Program Files\Python36\lib\site-packages\pandas\core\generic.py", line 1645, in _get_item_cache
values = self._data.get(item)
File "C:\Program Files\Python36\lib\site-packages\pandas\core\internals.py", line 3590, in get
loc = self.items.get_loc(item)
File "C:\Program Files\Python36\lib\site-packages\pandas\core\indexes\base.py", line 2444, in get_loc
return self._engine.get_loc(self._maybe_cast_indexer(key))
File "pandas\_libs\index.pyx", line 132, in pandas._libs.index.IndexEngine.get_loc (pandas\_libs\index.c:5280)
File "pandas\_libs\index.pyx", line 154, in pandas._libs.index.IndexEngine.get_loc (pandas\_libs\index.c:5126)
File "pandas\_libs\hashtable_class_helper.pxi", line 1210, in pandas._libs.hashtable.PyObjectHashTable.get_item (pandas\_libs\hashtable.c:20523)
File "pandas\_libs\hashtable_class_helper.pxi", line 1218, in pandas._libs.hashtable.PyObjectHashTable.get_item (pandas\_libs\hashtable.c:20477)
KeyError: 'C'
根據我的理解，這是發生的，因爲第一次列C不存在，所以移動列拋出此異常。
我的問題是否有解決此問題的替代方法？
呃..你創建了一個DF沒有 'C' 欄，讓你得到一個'KeyError'意料之中。什麼是預期的輸出？你不應該使用'B'列嗎？ – EdChum
您是不是指'np.where（df ['A']> df ['B']。shift（），df ['B']。shift（），df ['A']）'？ –
我需要這種方式。因此，'df.loc [0：'C']'可以是'0'或'df ['A']'，然後是'df.loc [1：'C']''df ['C' ] = np.where（df ['A']> df ['C']。shift（），df ['C']。shift（），df ['A']]'接管 – arkochhar