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, Feb 13 '23 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, Feb 13 '23 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, Feb 13 '23 at 21:04
One place to start is `zip(list_1, list_2)`. This will give you a list of tuples where each tuple contains a number and a list. Now you will need to transform the tuples into a single list. — Code-Apprentice, Feb 13 '23 at 21:06
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](https://stackoverflow.com/questions/6473679/transpose-list-of-lists) (just do `col_data = [list_1, *list_2]` first) — Pranav Hosangadi, Feb 13 '23 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, Feb 13 '23 at 21:59

Alexander Khomenko · Answer 1 · 2023-02-13T21:45:24.510

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 '23 at 21:45

answered Feb 13 '23 at 21:10

Alexander Khomenko

569
1
5
13

1

@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 ;-) – Alexander Khomenko Feb 13 '23 at 21:24

score 1 · Accepted Answer · answered Feb 13 '23 at 21:09

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 '23 at 21:09

Code-Apprentice

81,660
23
145
268

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

2 Answers2