我在ndf = df.melt（id_vars ='Country'，var_name ='Year'，value_name ='Obesity（％）'

Posted 2023-01-14

Traceback (most recent call last):

 File "C:\Users\fachr\Anaconda3\lib\site-packages\pandas\core\indexes\base.py", line 2646, in get_loc
return self._engine.get_loc(key)

 File "pandas\_libs\index.pyx", line 111, in pandas._libs.index.IndexEngine.get_loc

 File "pandas\_libs\index.pyx", line 138, in pandas._libs.index.IndexEngine.get_loc

 File "pandas\_libs\hashtable_class_helper.pxi", line 1619, in pandas._libs.hashtable.PyObjectHashTable.get_item

 File "pandas\_libs\hashtable_class_helper.pxi", line 1627, in pandas._libs.hashtable.PyObjectHashTable.get_item

KeyError: 'Country'


During handling of the above exception, another exception occurred:

Traceback (most recent call last):

 File "<ipython-input-57-97bd8d719664>", line 1, in <module>
     ndf = df.melt(id_vars='Country', var_name='Year', value_name='Obesity (%)')

 File "C:\Users\fachr\Anaconda3\lib\site-packages\pandas\core\frame.py", line 6506, in melt
    col_level=col_level,

 File "C:\Users\fachr\Anaconda3\lib\site-packages\pandas\core\reshape\melt.py", line 108, in melt
    id_data = frame.pop(col)

 File "C:\Users\fachr\Anaconda3\lib\site-packages\pandas\core\generic.py", line 790, in pop
    result = self[item]

 File "C:\Users\fachr\Anaconda3\lib\site-packages\pandas\core\frame.py", line 2800, in __getitem__
    indexer = self.columns.get_loc(key)

 File "C:\Users\fachr\Anaconda3\lib\site-packages\pandas\core\indexes\base.py", line 2648, in get_loc
    return self._engine.get_loc(self._maybe_cast_indexer(key))

 File "pandas\_libs\index.pyx", line 111, in pandas._libs.index.IndexEngine.get_loc

 File "pandas\_libs\index.pyx", line 138, in pandas._libs.index.IndexEngine.get_loc

 File "pandas\_libs\hashtable_class_helper.pxi", line 1619, in pandas._libs.hashtable.PyObjectHashTable.get_item

 File "pandas\_libs\hashtable_class_helper.pxi", line 1627, in pandas._libs.hashtable.PyObjectHashTable.get_item

KeyError: 'Country'

**我的代码**

#cleaning and restructuring data
import numpy as np 
import pandas as pd 

df = pd.read_csv('data.csv')
df.head()
df.shape 

df.iloc[0,1]
df.columns

df.drop([0,1,2],inplace=True)
df.head()

df.reset_index(drop=True, inplace = True)
df.head()

df.rename(columns='Unnamed : 0' : 'Country', inplace = True)
df.head

ndf = df.melt('Country', var_name='Year', value_name='Obesity (%)') 
ndf[['Year', 'Sex']] = ndf['Year'].str.split('.', expand=True)
ndf.head(10)

ndf=ndf.sort_values(by=['Country','Year'])

ndf=ndf.reset_index(drop=True)
ndf.head()

ndf['Sex']=ndf['Sex'].map(None: 'Both sexes', '1': 'Male', '2':'Female')

ndf['Age standardized estimate']=ndf['Obesity (%)'].apply(lambda x:x.split()[1])

ndf['Obesity (%)']=ndf['Obesity (%)'].apply(lambda x:x.split()[0])
ndf.head()
ndf.to_csv('obesity-clean-split.csv')

答案

如文档中所述，id_vars的pandas.DataFrame.melt关键字接受tuple，list或ndarray作为输入，而不是如您所愿的字符串。您必须在其中包含密钥方括号使其成为列表

将引发错误的行更改为：

# Take note of the [] around 'Country'
ndf = df.melt(['Country'], var_name='Year', value_name='Obesity (%)')