Python: write set of lists (1 nested list) to csv file

Question

I have a set of data with two lists. list_2 can have any number of nested lists in it (which is where my problem stems from).

list_1 = [2000.0, 2100.0, 2200.0]
list_2 = [[-1.86, 0.49, 1.36], [-1.29, 0.59, 1.62], [-.99, 0.19, 1.76]]

once in the csv file it should look like

2000    -1.86    -1.29    -.99
2100    0.49    0.59     0.19
2200    1.36     1.62     1.76

I have tried a few different ways of writing the file

    with open(file_name, 'w') as file:
        writer = csv.writer(file)
        writer.writerows(zip(list_1, list_2))

I've also tried zipping them before as see in this question

I've also tried separating the lists (in list_2) but that does not allow for any growth. I do not know the number of nested lists before running the application so it has to be able to grow.

writer.writerows(zip(list_1, list_2, list_3, list_4))  # does not allow for dynamic growth

show how should look csv for a more deeper nesting, say 4 levels — RomanPerekhrest
– RomanPerekhrest, Commented Feb 13, 2023 at 21:02
If you don't know the number of lists, you should be using a list of lists, not individually numbered list variables. — chepner
– chepner, Commented Feb 13, 2023 at 21:02
@chepner Yes that's what I'm trying to do. The last example was just to show what I have tried and what didn't work for me — Luke
– Luke, Commented Feb 13, 2023 at 21:04
You have a list of data in column-major format. csv.writerows can write a row-major list-of-lists. You can do this by transposing your data. Does this answer your question? Transpose list of lists (just do col_data = [list_1, *list_2] first) — pho
– pho, Commented Feb 13, 2023 at 21:07
In each case pay attention to add newline='' in order to avoid empty rows: with open(file_name, 'w', newline='') — Alexander Khomenko
– Alexander Khomenko, Commented Feb 13, 2023 at 21:59

Alexander Khomenko · Accepted Answer · 2023-02-13 21:45:24Z

3

if I get you right you don't know how many lists you are going to have. But all of them will have the same size?

And you want them to be stored "vertically"?

I have the feeling a transpose operation would help you very well.

import csv
import numpy

list_1 = [2000.0, 2100.0, 2200.0]
list_2 = [[-1.86, 0.49, 1.36], [-1.29, 0.59, 1.62], [-.99, 0.19, 1.76]]

list_3 = [list_1] + list_2
output_array = numpy.transpose(numpy.array(list_3))

with open(file_name, 'w', newline='') as file:
    writer = csv.writer(file)
    writer.writerows(output_array)

edited Feb 13, 2023 at 21:45

answered Feb 13, 2023 at 21:10

Alexander Khomenko

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Alexander Khomenko Over a year ago

@PranavHosangadi for me it is mostly enough to get an idea how to solve a situation. But if you ask I will extend the answer ;-)

Code-Apprentice · Accepted Answer · 2023-02-13 21:09:01Z

1

You can do this with the * operator:

zip(list_1, *list_2)

This will create a list of lists where the first element of each sub list comes from list_1 and the remaining elements come from each of the lists in list_2.

answered Feb 13, 2023 at 21:09

Code-Apprentice

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