Append a column to an existing csv file in python

Question

This question has been asked before but those solutions didn't work for me. I have a csv file, example.csv, with data in the following format:

grid,u,lambda
0.0,0.0,-93000
0.01,-0.01,-93000
0.02,0.05,-93000

Now I have a function f.fraction('function') which returns me [1.00000000e+00 1.00000000e+00 1.00000000e+00]. I want to append this to the same file, example.csv. the final result:

grid,u,lambda,new_function
0.0,0.0,-93000,1.00000000e+00
0.01,-0.01,-93000,1.00000000e+00
0.02,0.05,-93000,1.00000000e+00

How can I do this?

Diego Ramirez Vasquez · Accepted Answer · 2021-06-20 23:24:14Z

1

you can read the file first using pandas, append the new column and then save it.

import pandas as pd
df = pd.read_csv('example.csv')
df['new_function'] = f.fraction('function')
df.to_csv('example.csv')

answered Jun 20, 2021 at 23:24

Diego Ramirez Vasquez

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3 Comments

Emotional Damage Over a year ago

Thank you for this solution. This worked perfectly fine. But, if you don't mind can you also provide the solution without using pandas as well, please?. I mean by using import csv. @diego-ramirez-vasquez

Diego Ramirez Vasquez Over a year ago

This post will help you to do it without pandas :) stackoverflow.com/questions/60465764/…

Emotional Damage Over a year ago

Thanks again! @Diego Ramirez Vasquez

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