在groupby操作期间重命名pandas数据框中的列

Question

I tried to rename the column that has been obtained as the result of groupby & count operation like below:

dfa = df.groupby('Product_ID').Product_ID.count().rename(columns={0: "Product",1:"Sale_count"}).reset_index()
print(dfa[:1])

the output obtained is

 Product_ID     0
0  P00000142  1130

The column names are not what I specified. So I changed it again using the below command

dfa.columns =['product','sales']
print(dfa[:1])

 product  sales
0  P00000142   1130

Then I got the expected column names. However I believe it shall be obtained during the first method dataframe.rename itself. What is wrong in the 1st code snippet dfa = df.groupby('Product_ID').Product_ID.count().rename(columns={0: "Product",1:"Sale_count"}).reset_index() that I did not get the expected output.

Answer 1

如评论中所述，您需要：

df.groupby('Product_ID').size().reset_index(name='sales_count')