Saving a list containing a numpy array in CSV format in Python

Question

I am trying to save a list sigma1 containing a numpy array in CSV format. In the current output, the data is saved in multiple rows without commas. In the expected output, I want the data to be saved in a single row with commas, exactly like sigma1.

import numpy as np
import csv

sigma1= [np.array([[0.02109],
       [0.02109],
       [0.02109],
       [0.02109],
       [0.02109],
       [0.02109],
       [0.02109],
       [0.02109],
       [0.02109],
       [0.02109],
       [0.02109],
       [0.02109]])]


with open('Data_sigma.csv', 'w') as f:
     writer = csv.writer(f)
     print(sigma1)
     f.writelines('sigma'+ '\n')
     f.write(str(sigma1))

The current output is

The expected output is

If you write out the NumPy array to your CSV file the expected output will simply contain each value separated by a comma (no np.array) i.e. [0.02109],[0.02109],[0.02109],[0.02109],[0.02109],[0.02109],[0.02109],[0.02109],[0.02109],[0.02109],[0.02109],[0.02109] — Prins
– Prins, Commented Aug 31, 2022 at 6:10

Prins · Accepted Answer · 2022-08-31 06:05:48Z

1

In your code, you are using the file to write your lines rather than the csv writer. Use the csv writer with the writerow function to write a single row to the CSV file:

with open('Data_sigma.csv', 'w') as f:
     writer = csv.writer(f)
     writer.writerow(sigma1[0])

Note, as sigma1 is a list containing the NumPy array, we have written out sigma1[0]. If you have multiple NumPy arrays in sigma1 then you can write all of these out to your file using writerows as follows:

with open('Data_sigma.csv', 'w') as f:
     writer = csv.writer(f)
     writer.writerows(sigma1)

edited Aug 31, 2022 at 6:05

answered Aug 31, 2022 at 6:00

Prins

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