python错误与apply功能

Question

我有下面的示例数据和代码，在这里试图遍历dataDF列并找到3个递增值的第一种情况，然后从dataDF列返回与第3个递增值相对应的Quarter值。 我在下面出现错误，我不确定为什么。 我真的是python新手，欢迎任何提示。

样本数据：

 return dataDF.head(20).to_dict() 

{'Quarter': {246: '2008q3',
 247: '2008q4',
 248: '2009q1',
 249: '2009q2',
 250: '2009q3',
 251: '2009q4',
 252: '2010q1',
 253: '2010q2',
 254: '2010q3',
 255: '2010q4',
 256: '2011q1',
 257: '2011q2',
 258: '2011q3',
 259: '2011q4',
 260: '2012q1',
 261: '2012q2',
 262: '2012q3',
 263: '2012q4',
 264: '2013q1',
 265: '2013q2'},
 'dataDF': {246: 14843.0,
 247: 14549.9,
 248: 14383.9,
 249: 14340.4,
 250: 14384.1,
 251: 14566.5,
 252: 14681.1,
 253: 14888.6,
 254: 15057.700000000001,
 255: 15230.200000000001,
 256: 15238.4,
 257: 15460.9,
 258: 15587.1,
 259: 15785.299999999999,
 260: 15973.9,
 261: 16121.9,
 262: 16227.9,
 263: 16297.299999999999,
 264: 16475.400000000001,
 265: 16541.400000000001}}

码：

 def get_end:
    dataDF = pd.ExcelFile('gdplev.xls').parse(skiprows=7)[['Unnamed: 4', 
'Unnamed: 5']].loc[246:]
    dataDF.columns = ['Quarter','dataDF']
    dataDF['dataDF'] = pd.to_numeric(dataDF['dataDF'])

    def find_end(x):
        qrts = []
        if (dataDF < dataDF.shift()) & (dataDF.shift(periods=1) < 
 dataDF.shift(periods=2)):
            qrts.append(dataDF.shift(2)[0])
        return qrts

    qrts = dataDF.loc[:(len(dataDF) - 2)].apply(find_end)
    return qrts[0]

get_end

错误：

       ---------------------------------------------------------------------------
    KeyError                                  Traceback (most recent call last)
    /opt/conda/lib/python3.5/site-packages/pandas/indexes/base.py in 
    get_loc(self, key, method, tolerance)
       1944             try:
    -> 1945                 return self._engine.get_loc(key)
       1946             except KeyError:

    pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4154)()

    pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4018)()

    pandas/hashtable.pyx in pandas.hashtable.PyObjectHashTable.get_item 
    (pandas/hashtable.c:12368)()

    pandas/hashtable.pyx in pandas.hashtable.PyObjectHashTable.get_item 
    (pandas/hashtable.c:12322)()

    KeyError: 0

    During handling of the above exception, another exception occurred:

    KeyError                                  Traceback (most recent call last)
    <ipython-input-14-e2cd3908b4c4> in <module>()
         20 
         21 
    ---> 22 get_recession_end()
         23 

    <ipython-input-14-e2cd3908b4c4> in get_recession_end()
         15 
         16     quarters = dataDF.loc[:(len(dataDF) - 2)].apply(do_the_foo)
    ---> 17     return quarters[0]
         18     # return dataDF.head(20).to_dict()
         19 

        /opt/conda/lib/python3.5/site-packages/pandas/core/frame.py in 
        __getitem__(self, key)
           1995             return self._getitem_multilevel(key)
           1996         else:
         -> 1997             return self._getitem_column(key)
          1998 
       1999     def _getitem_column(self, key):

    /opt/conda/lib/python3.5/site-packages/pandas/core/frame.py in 
    _getitem_column(self, key)
       2002         # get column
       2003         if self.columns.is_unique:
    -> 2004             return self._get_item_cache(key)
       2005 
       2006         # duplicate columns & possible reduce dimensionality

    /opt/conda/lib/python3.5/site-packages/pandas/core/generic.py in 
    _get_item_cache(self, item)
           1348         res = cache.get(item)
           1349         if res is None:
        -> 1350             values = self._data.get(item)
           1351             res = self._box_item_values(item, values)
           1352             cache[item] = res

    /opt/conda/lib/python3.5/site-packages/pandas/core/internals.py in get(self, 
   item, fastpath)
       3288 
       3289             if not isnull(item):
    -> 3290                 loc = self.items.get_loc(item)
       3291             else:
       3292                 indexer = np.arange(len(self.items))
    [isnull(self.items)]

    /opt/conda/lib/python3.5/site-packages/pandas/indexes/base.py in 
    get_loc(self, key, method, tolerance)
       1945                 return self._engine.get_loc(key)
       1946             except KeyError:
    -> 1947                 return 
    self._engine.get_loc(self._maybe_cast_indexer(key))
       1948 
       1949         indexer = self.get_indexer([key], method=method, 
    tolerance=tolerance)

    pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4154)()

    pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4018)()

    pandas/hashtable.pyx in pandas.hashtable.PyObjectHashTable.get_item 
    (pandas/hashtable.c:12368)()

    pandas/hashtable.pyx in pandas.hashtable.PyObjectHashTable.get_item 
    (pandas/hashtable.c:12322)()

    KeyError: 0

Answer 1

该错误意味着熊猫无法找到列标签“ 0”，因为df ['label']意味着要访问列。

您应该使用df.loc [0，：]访问标签为0的行。如果要访问位置0的行，请使用df.iloc [0，：]。

一些技巧：

• 始终使用.loc []或.iloc []，请勿使用[]。

• 避免递归，而是使用循环。