如何将熊猫数据帧附加到具有不同列的_csv

Question

I have a pandas data frame read from csv file (data.csv). After processing data, I have another data frame less number of columns than in the data.csv file but still has same column name. Now I want to append new data frame to data.csv file.
I don't know how to append and merge by column name.

data.csv file has structure

ID    name   email  
1     John   j@gmail.com  
2     Ann    a@gmail.com  

New data frame has structure

ID    name  
1     Smith  
2     Kov  
3     Jane  

Now I want to write new data frame to data.csv file, result must be

ID     Name      email  
1      John      j@gmail.com  
2      Ann       a@gmail.com  
3      Smith   
4      Kov  
5      Jane  

Answer 1

The approach here isn't to append the existing csv, but rather to write over it, in this case with the original data as part of your output. If you read your original csv as df and your new dataframe is df2 :

df3 = df.append(df2)
df3.to_csv("data.csv")

or on one line:

df.append(df2).to_csv("data.csv")

The pd.DataFrame.append method works how you want it to when the column names match. Of course, I would recommend saving to another filename at first to make sure you're getting the output you want, and once you're happy with it changing your code to overwrite data.csv, lest you accidentally destroy data.