python-熊猫:如何按日期选择
在这种情况下,为什么我可以按月份进行选择,而不能按日期进行选择python-熊猫:如何按日期选择,python,pandas,Python,Pandas,在这种情况下,为什么我可以按月份进行选择,而不能按日期进行选择 dates = pd.date_range( start = "01/01/1931" , end = "01/02/1941" ) new_df_4 = new_df_3.reindex(dates) new_df_4["1931-10"][![enter image description here][1]][1] 但这不起作用: new_df_4["1931-10-02"] KeyError回溯最近一次呼叫last
dates = pd.date_range( start = "01/01/1931" , end = "01/02/1941" )
new_df_4 = new_df_3.reindex(dates)
new_df_4["1931-10"][![enter image description here][1]][1]
但这不起作用:
new_df_4["1931-10-02"]
KeyError回溯最近一次呼叫last
在里面
-->1新的_df_4[1931-10-02]
/Users/romain/anaconda/lib/python2.7/site-packages/pandas/core/frame.pyc in __getitem__(self, key)
1990 return self._getitem_multilevel(key)
1991 else:
-> 1992 return self._getitem_column(key)
1993
1994 def _getitem_column(self, key):
/Users/romain/anaconda/lib/python2.7/site-packages/pandas/core/frame.pyc in _getitem_column(self, key)
2002 result = self._constructor(self._data.get(key))
2003 if result.columns.is_unique:
-> 2004 result = result[key]
2005
2006 return result
/Users/romain/anaconda/lib/python2.7/site-packages/pandas/core/frame.pyc in __getitem__(self, key)
1990 return self._getitem_multilevel(key)
1991 else:
-> 1992 return self._getitem_column(key)
1993
1994 def _getitem_column(self, key):
/Users/romain/anaconda/lib/python2.7/site-packages/pandas/core/frame.pyc in _getitem_column(self, key)
1997 # get column
1998 if self.columns.is_unique:
-> 1999 return self._get_item_cache(key)
2000
2001 # duplicate columns & possible reduce dimensionality
/Users/romain/anaconda/lib/python2.7/site-packages/pandas/core/generic.pyc in _get_item_cache(self, item)
1343 res = cache.get(item)
1344 if res is None:
-> 1345 values = self._data.get(item)
1346 res = self._box_item_values(item, values)
1347 cache[item] = res
/Users/romain/anaconda/lib/python2.7/site-packages/pandas/core/internals.pyc in get(self, item, fastpath)
3223
3224 if not isnull(item):
-> 3225 loc = self.items.get_loc(item)
3226 else:
3227 indexer = np.arange(len(self.items))[isnull(self.items)]
/Users/romain/anaconda/lib/python2.7/site-packages/pandas/indexes/base.pyc in get_loc(self, key, method, tolerance)
1876 return self._engine.get_loc(key)
1877 except KeyError:
-> 1878 return self._engine.get_loc(self._maybe_cast_indexer(key))
1879
1880 indexer = self.get_indexer([key], method=method, tolerance=tolerance)
pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4027)()
pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:3891)()
pandas/hashtable.pyx in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:12408)()
pandas/hashtable.pyx in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:12359)()
KeyError: '1931-10-02'
对于“按月选择”,请使用:
如果来自以下位置的分辨率相同,则此操作无效:
警告
但是,如果字符串被视为完全匹配,则
DataFrame的[]中的选择将按列而不是按行进行,请参阅
索引基础。例如,dft_分钟['2011-12-31 23:59']将升高
“2012-12-31 23:59”的KeyError与索引和
没有这样名称的列:始终具有明确的
选择,无论行被视为切片还是单个
选择,使用.loc
In [95]: dft_minute.loc['2011-12-31 23:59']
Out[95]:
a 1
b 4
Name: 2011-12-31 23:59:00, dtype: int64
如果需要,可以使用“按日期选择”:
new_df_4.loc["1931-10-02"]
样本:
np.random.seed(10)
dates = pd.date_range( start = "01/01/1931" , end = "01/02/1941" )
new_df_4 = pd.DataFrame({'a':np.random.randint(10, size=len(dates))}, index=dates)
print (new_df_4.head())
a
1931-01-01 9
1931-01-02 4
1931-01-03 0
1931-01-04 1
1931-01-05 9
print (new_df_4["1931-10"])
a
1931-10-01 9
1931-10-02 6
1931-10-03 9
1931-10-04 7
1931-10-05 8
1931-10-06 0
1931-10-07 9
1931-10-08 6
1931-10-09 0
1931-10-10 1
1931-10-11 0
...
print (new_df_4.loc["1931-10-02"])
a 6
Name: 1931-10-02 00:00:00, dtype: int32
对于“按月选择”,请使用:
如果来自以下位置的分辨率相同,则此操作无效:
警告
但是,如果字符串被视为完全匹配,则
DataFrame的[]中的选择将按列而不是按行进行,请参阅
索引基础。例如,dft_分钟['2011-12-31 23:59']将升高
“2012-12-31 23:59”的KeyError与索引和
没有这样名称的列:始终具有明确的
选择,无论行被视为切片还是单个
选择,使用.loc
In [95]: dft_minute.loc['2011-12-31 23:59']
Out[95]:
a 1
b 4
Name: 2011-12-31 23:59:00, dtype: int64
如果需要,可以使用“按日期选择”:
new_df_4.loc["1931-10-02"]
样本:
np.random.seed(10)
dates = pd.date_range( start = "01/01/1931" , end = "01/02/1941" )
new_df_4 = pd.DataFrame({'a':np.random.randint(10, size=len(dates))}, index=dates)
print (new_df_4.head())
a
1931-01-01 9
1931-01-02 4
1931-01-03 0
1931-01-04 1
1931-01-05 9
print (new_df_4["1931-10"])
a
1931-10-01 9
1931-10-02 6
1931-10-03 9
1931-10-04 7
1931-10-05 8
1931-10-06 0
1931-10-07 9
1931-10-08 6
1931-10-09 0
1931-10-10 1
1931-10-11 0
...
print (new_df_4.loc["1931-10-02"])
a 6
Name: 1931-10-02 00:00:00, dtype: int32
这是一个转折点,但并没有回答这个问题:-/@romainjouin它实际上不是一个解决方法,它是这样设计的,所以如果你想按索引选择,你需要使用.loc。请参见编辑中的警告。这是一个转折点,但没有回答问题:-/@romainjouin它实际上不是一个解决方法,它是这样设计的,因此如果要按索引选择,则需要使用.loc。有关警告,请参见编辑。