如何在python中基于Where函数获取两列值

Question

问题是： 基于user_id列，我想得到rating和{}列的值。可能有多个条目具有相同的用户标识。我希望获取具有rating和product_id列值的所有用户记录，但对于用户未对电影进行评级的电影，应将其显示为Nan，但仍应检索product_id。下表提供了一些数据。在

| product_id  | user_id         | user_name                                    | rating |
|-------------|-----------------|----------------------------------------------|--------|
|  B0009XRZ92 | A2JFZLAUG3YFQ7  |  Entropy Babe "EB"                           | 5      |
|  B0009XRZ92 | A22HGAAO8KZ2N3  |  R.   Metzelar                               | 5      |
|  B000067A8B |  A2NJO6YE954DBH |  Lawrance M. Bernabo                         | 4      |
|  B0009XRZ92 |  A3HE4MYMWK4AER |  Rebecca M. Eddy "Foster Mom and   Untbunny" | 5      |
|  B003A3R3ZY | A9A2PR663ED1V   |  Roger D. Goff                               | 5      |
|  B0009XRZ92 | A2MRZDJF90JC1U  |  Suzanne K. Armstrong "Suzy Q"               | 5      |
|  B0009XRZ92 |  A2YNBDT3170PCR |  C.   O'Hern                                 | 5      |
|  B0009XRZ92 |  A10VJ7BDVCPKEZ |  Carol S. Bottom                             | 5      |
|  B0009XRZ92 |  AAAQO894MG80B  |  Paul J. Michko                              | 5      |
|  B00067BBQE | A9A2PR663ED1V   |  Roger D. Goff                               | 5      |
|  B0009XRZ92 | A31S5QUMFR8NH2  |  Dana L. Jordan "Mom of Twins"               | 5      |
|  B0009XRZ92 |  A2DS24DHXUH0GM |  Gaz    Rev(iewer)                           | 4      |
|  B00006AUMZ |  A2NJO6YE954DBH |  Lawrance M. Bernabo                         | 4      |
|  B0009XRZ92 |  A16FRHL2ZC7EUR |  M.   Claytor                                | 5      |
|  B0009XRZ92 | A3AV8R0A62PP1N  |  MARCUSHELBLINZ "mmmacman"                   | 5      |
|  B0009XRZ92 |  A3QN84C38DE9FU |  Gillian M. Kratzer                          | 5      |
|  B0009XRZ92 |  A36MLTLVQFEQYL |  Yossarian "alienated socialist"             | 5      |
|  B00006AUMD |  A2NJO6YE954DBH |  Lawrance M. Bernabo                         | 4      |

What I want to do is:

To take one user_id at a time and display the rating and product_id columns value for that user for all the movies in the table and if the user didn't rate some movies then the record should be displayed with the product_id value and rating as Nan and the whole process should be repeated for all the users.

例如，user_id: A2NJO6YE954DBH的记录如下所示：

^{pr2}$

我试着用Pandas库来编写代码，但还是忍不住。这是我所做的一切，但它没有输出我想要的。在

import pandas as pd
df =pd.read_csv('out.csv')
unique_users=df.user_id.unique()
for x, y in enumerate(unique_users):
    print(df[['rating','product_id']].where(df.user_id==y))

请帮帮我。。谢谢

Answer 1

如果我理解正确，您可以在此处使用^{}：

df_new=df.pivot_table(index='user_id',columns='product_id',values='rating').rename_axis(None,1)
print(df_new)


                     B000067A8B     B00006AUMD     B00006AUMZ     B00067BBQE   \
user_id                                                                         
  A10VJ7BDVCPKEZ             NaN            NaN            NaN            NaN   
  A16FRHL2ZC7EUR             NaN            NaN            NaN            NaN   
  A2DS24DHXUH0GM             NaN            NaN            NaN            NaN   
  A2NJO6YE954DBH             4.0            4.0            4.0            NaN   
  A2YNBDT3170PCR             NaN            NaN            NaN            NaN   
  A36MLTLVQFEQYL             NaN            NaN            NaN            NaN   
  A3HE4MYMWK4AER             NaN            NaN            NaN            NaN   
  A3QN84C38DE9FU             NaN            NaN            NaN            NaN   
  AAAQO894MG80B              NaN            NaN            NaN            NaN   
 A22HGAAO8KZ2N3              NaN            NaN            NaN            NaN   
 A2JFZLAUG3YFQ7              NaN            NaN            NaN            NaN   
 A2MRZDJF90JC1U              NaN            NaN            NaN            NaN   
 A31S5QUMFR8NH2              NaN            NaN            NaN            NaN   
 A3AV8R0A62PP1N              NaN            NaN            NaN            NaN   
 A9A2PR663ED1V               NaN            NaN            NaN            5.0   

                     B0009XRZ92     B003A3R3ZY   
user_id                                          
  A10VJ7BDVCPKEZ             5.0            NaN  
  A16FRHL2ZC7EUR             5.0            NaN  
  A2DS24DHXUH0GM             4.0            NaN  
  A2NJO6YE954DBH             NaN            NaN  
  A2YNBDT3170PCR             5.0            NaN  
  A36MLTLVQFEQYL             5.0            NaN  
  A3HE4MYMWK4AER             5.0            NaN  
  A3QN84C38DE9FU             5.0            NaN  
  AAAQO894MG80B              5.0            NaN  
 A22HGAAO8KZ2N3              5.0            NaN  
 A2JFZLAUG3YFQ7              5.0            NaN  
 A2MRZDJF90JC1U              5.0            NaN  
 A31S5QUMFR8NH2              5.0            NaN  
 A3AV8R0A62PP1N              5.0            NaN  
 A9A2PR663ED1V               NaN            5.0

Answer 2

试试看

 print(df[df.user_id==y][['rating','product_id']])

Answer 3

您可以提取user_id等于特定值的行，方法是：

import pandas as pd
df = pd.read_csv('out.csv')
unique_users = df.user_id.unique()
for x, y in enumerate(unique_users):
    print(df.loc[df['user_id'] == y])