Estoy probando el siguiente código
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) El supuesto es que la primera operación df['C].shift() debe asumir como 0 (ya que df['C'] no existe)
Rendimiento esperado
ABC 0 23 52 23 1 36 49 36 2 12 61 36 3 75 82 75 4 70 12 75
pero estoy recibiendo una excepción KeyError.
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 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'
Según tengo entendido, esto está sucediendo, porque por primera vez la Columna C no existe, por lo que al desplazar la columna se produce esta excepción.
Mis preguntas ¿hay una forma alternativa de resolver este problema?
necesitas cummax
df['C'] = df.A.cummax()