确定列的累积最大值 [英] Determining the cumulative maximum of a column
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问题描述
我正在尝试以下代码
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)
假设第一个df['C].shift()
操作应假定为0(因为df['C']
不存在)
Assumption is that first df['C].shift()
operation should assume as 0 (since df['C']
is non existent)
预期输出
A B C
0 23 52 23
1 36 49 36
2 12 61 36
3 75 82 75
4 70 12 75
但是我遇到了KeyError异常.
but I'm getting a KeyError exception.
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'
据我了解,这种情况正在发生,因为列C首次不存在,因此移动列会引发此异常.
As per my understanding this is happening, because for the first time Column C is non existent, so shifting the column throws this exception.
我的问题是否有解决此问题的替代方法?
My questions is there an alternate way of solving this problem?
推荐答案
您需要cummax
:
df['C'] = df.A.cummax()
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