python - 值错误: cannot reindex from a duplicate axis using groupy and apply pct_change in Pandas

Question

我尝试计算groupby pct_change使用df.groupby('type')['value'].apply(lambda x: x.pct_change())对于数据框。

但它会生成ValueError: cannot reindex from a duplicate axis ，有什么想法如何处理这个问题吗？谢谢。

Answer 1

如果我的索引中有重复项，我会收到同样的错误。您需要reset_index():

In [726]: df.append(df)                                                                                                                                                                        
Out[726]: 
  customer brand product  quantity  price  new_quantity
0       C1    B1      P1       100      5           500
1       C1    B1      P2        10     20           200
2       C1    B2      P3        50      7           350
3       C2    B1      P1        75      5           375
4       C2    B2      P3         5      7            35
0       C1    B1      P1       100      5           500
1       C1    B1      P2        10     20           200
2       C1    B2      P3        50      7           350
3       C2    B1      P1        75      5           375
4       C2    B2      P3         5      7            35

df.groupby('customer')['quantity'].apply(lambda x: x.pct_change()) 

# ValueError: cannot reindex from a duplicate axis

In [730]: df.append(df).reset_index().groupby('customer')['quantity'].apply(lambda x: x.pct_change())                                                                                          
Out[730]: 
0          NaN
1    -0.900000
2     4.000000
3          NaN
4    -0.933333
5     1.000000
6    -0.900000
7     4.000000
8    14.000000
9    -0.933333
Name: quantity, dtype: float64