ValueError:只能传递带有布尔值的DataFrame

Question

问题

在这个数据文件中，使用“REGION”列将美国分为四个地区。

创建一个查询，查找属于区域1或区域2的县，其名称以“Washington”开头，并且其popestimate105大于其popestimate104。

此函数应返回一个5x2数据帧，其中列=['STNAME'，'CTYNAME']和与人口普查数据框相同的索引ID（按索引升序排序）。

代码

    def answer_eight():
    counties=census_df[census_df['SUMLEV']==50]
    regions = counties[(counties[counties['REGION']==1]) | (counties[counties['REGION']==2])]
    washingtons = regions[regions[regions['COUNTY']].str.startswith("Washington")]
    grew = washingtons[washingtons[washingtons['POPESTIMATE2015']]>washingtons[washingtons['POPESTIMATES2014']]]
    return grew[grew['STNAME'],grew['COUNTY']]

outcome = answer_eight()
assert outcome.shape == (5,2)
assert list (outcome.columns)== ['STNAME','CTYNAME']
print(tabulate(outcome, headers=["index"]+list(outcome.columns),tablefmt="orgtbl"))

错误

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-77-546e58ae1c85> in <module>()
      6     return grew[grew['STNAME'],grew['COUNTY']]
      7 
----> 8 outcome = answer_eight()
      9 assert outcome.shape == (5,2)
     10 assert list (outcome.columns)== ['STNAME','CTYNAME']

<ipython-input-77-546e58ae1c85> in answer_eight()
      1 def answer_eight():
      2     counties=census_df[census_df['SUMLEV']==50]
----> 3     regions = counties[(counties[counties['REGION']==1]) | (counties[counties['REGION']==2])]
      4     washingtons = regions[regions[regions['COUNTY']].str.startswith("Washington")]
      5     grew = washingtons[washingtons[washingtons['POPESTIMATE2015']]>washingtons[washingtons['POPESTIMATES2014']]]

/opt/conda/lib/python3.5/site-packages/pandas/core/frame.py in __getitem__(self, key)
   1991             return self._getitem_array(key)
   1992         elif isinstance(key, DataFrame):
-> 1993             return self._getitem_frame(key)
   1994         elif is_mi_columns:
   1995             return self._getitem_multilevel(key)

/opt/conda/lib/python3.5/site-packages/pandas/core/frame.py in _getitem_frame(self, key)
   2066     def _getitem_frame(self, key):
   2067         if key.values.size and not com.is_bool_dtype(key.values):
-> 2068             raise ValueError('Must pass DataFrame with boolean values only')
   2069         return self.where(key)
   2070 

ValueError: Must pass DataFrame with boolean values only

我一无所知。我哪里做错了？

谢谢

Answer 1

你试图使用不同形状的df来掩盖你的df，这是错误的，另外，你通过条件的方式被错误地使用。将df中的列或序列与标量进行比较以生成布尔掩码时，应仅传递条件，而不是连续使用。

def answer_eight():
    counties=census_df[census_df['SUMLEV']==50]
    # this is wrong you're passing the df here multiple times
    regions = counties[(counties[counties['REGION']==1]) | (counties[counties['REGION']==2])]
    # here you're doing it again
    washingtons = regions[regions[regions['COUNTY']].str.startswith("Washington")]
    # here you're doing here again also
    grew = washingtons[washingtons[washingtons['POPESTIMATE2015']]>washingtons[washingtons['POPESTIMATES2014']]]
    return grew[grew['STNAME'],grew['COUNTY']]

你想要：

def answer_eight():
    counties=census_df[census_df['SUMLEV']==50]
    regions = counties[(counties['REGION']==1]) | (counties['REGION']==2])]
    washingtons = regions[regions['COUNTY'].str.startswith("Washington")]
    grew = washingtons[washingtons['POPESTIMATE2015']>washingtons['POPESTIMATES2014']]
    return grew[['STNAME','COUNTY']]