说我有以下数据框：
import pandas as pd
data = {'Year':[2018,2018,2018],'Month':[1,1,2,3,3],'ID':['A','A','B','B'],'Fruit':['Apple','Banana','Apple','Pear','Mango','Mango']}
df = pd.DataFrame(data,columns=['Year','Month','ID','Fruit'])
df = df.astype(str)
df
我想提取重复的“年”，“月”和“ ID”的组合。因此，使用上述数据框，预期结果就是该数据框：
我这样做的方法是首先执行groupby以计算Year，Month和ID的组合出现的次数：
df2 = df.groupby(['Year','Month'])['ID'].value_counts().to_frame(name = 'Count').reset_index()
df2 = df2[df2.Count>1]
df2
然后，我的想法是遍历groupby数据框中的Year，Month和ID组合，然后将与原始数据框中的组合匹配的那些行提取到新的数据框：
df_new = pd.DataFrame(columns=df.columns,index=range(sum(df2.Count)))
count = 0
for i in df2.index:
temp = df[(df.ID==df2.ID[i]) & (df.Year==df2.Year[i]) & (df.Month==df2.Month[i])]
temp.reset_index(drop=True,inplace=True)
for j in range(len(temp)):
df_new.iloc[count] = temp.iloc[j]
count+=1
df_new
但这会产生以下错误：
---------------------------------------------------------------------------
IndexError Traceback (most recent call last)
<ipython-input-38-7f2d95d71270> in <module>()
6 temp.reset_index(drop=True,inplace=True)
7 for j in range(len(temp)):
----> 8 df_new.iloc[count] = temp.iloc[j]
9 count+=1
10 df_new
c:\users\h473\appdata\local\programs\python\python35\lib\site-packages\pandas\core\indexing.py in __setitem__(self,key,value)
187 else:
188 key = com.apply_if_callable(key,self.obj)
--> 189 indexer = self._get_setitem_indexer(key)
190 self._setitem_with_indexer(indexer,value)
191
c:\users\h473\appdata\local\programs\python\python35\lib\site-packages\pandas\core\indexing.py in _get_setitem_indexer(self,key)
173
174 try:
--> 175 return self._convert_to_indexer(key,is_setter=True)
176 except TypeError as e:
177
c:\users\h473\appdata\local\programs\python\python35\lib\site-packages\pandas\core\indexing.py in _convert_to_indexer(self,obj,axis,is_setter)
2245
2246 try:
-> 2247 self._validate_key(obj,axis)
2248 return obj
2249 except ValueError:
c:\users\h473\appdata\local\programs\python\python35\lib\site-packages\pandas\core\indexing.py in _validate_key(self,axis)
2068 return
2069 elif is_integer(key):
-> 2070 self._validate_integer(key,axis)
2071 elif isinstance(key,tuple):
2072 # a tuple should already have been caught by this point
c:\users\h473\appdata\local\programs\python\python35\lib\site-packages\pandas\core\indexing.py in _validate_integer(self,axis)
2137 len_axis = len(self.obj._get_axis(axis))
2138 if key >= len_axis or key < -len_axis:
-> 2139 raise IndexError("single positional indexer is out-of-bounds")
2140
2141 def _getitem_tuple(self,tup):
IndexError: single positional indexer is out-of-bounds
怎么了？我不知道。
当我将for循环的内容更改为以下内容时，该错误消失，从而产生所需的结果：
for j in range(len(temp)):
df_new.ID[count] = temp.ID[j]
df_new.Year[count] = temp.Year[j]
df_new.Month[count] = temp.Month[j]
df_new.Fruit[count] = temp.Fruit[j]
count+=1
但这是一个繁琐的解决方法，涉及为原始数据帧中的每个n列编写n行。