Save list of lists as rows in csv file python

Question

I have a list of lists as follows:

L = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

I want to save this in a csv file as follows:

index, name, lists

0, 'name1', [1, 2, 3]
1, 'name2', [4, 5, 6]
2, 'name3', [7, 8, 9]

If this is possible, then how should I do this with python?

Have you read through the python csv module documentation? What have you tried? — glibdud
– glibdud, Commented Mar 29, 2019 at 19:56
@glibdud No I haven't read about the csv module but I tried writing to the file using python and the problem is that if I convert the sublists to a string, then the comma between them again acts as a separator and separates the sublist into more columns. I want the whole sublist to go in a single column — Se7eN
– Se7eN, Commented Mar 29, 2019 at 20:00
A comma separator value may be inappropriate in this case because to a parser, it's a bit ambiguous as what is a valid separator and what isn't when reading the file. A \t or tab-char may be more appropriate — C.Nivs
– C.Nivs, Commented Mar 29, 2019 at 20:03
I think the simplest would be to go and make a pandas dataframe and load your data in it and using to_csv function you can write it. — Yusuf Talha Tamer
– Yusuf Talha Tamer, Commented Mar 29, 2019 at 20:09

Nathaniel · Accepted Answer · 2019-03-29 20:10:46Z

2

You can use Pandas to assemble your data into a data frame and easily output it as a CSV file:

import pandas as pd

L = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
name = ['name1', 'name2', 'name3']

df = pd.DataFrame({'name': name, 'lists': L})
print(df)

df.to_csv('file.csv', index_label='index')

    name      lists
0  name1  [1, 2, 3]
1  name2  [4, 5, 6]
2  name3  [7, 8, 9]

answered Mar 29, 2019 at 20:10

Nathaniel

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4 Comments

Se7eN Over a year ago

When I load the csv and get the list like df['lists'][0] , it returns a list like [1 2 3] . How can I convert this to a list?

Nathaniel Over a year ago

Pandas is not the ideal tool for storing a list of lists. It looks like it is importing the text as a string.

Nathaniel Over a year ago

You can convert individual columns to a list like this: list(pd.eval(df['lists'][0])), which gives [1, 2, 3].

Se7eN Over a year ago

Turns out I was storing a numpy array and converting it to a list and then using pd.eval() on it worked. Thanks!

Skam · Accepted Answer · 2019-03-29 20:09:06Z

1

If you leave the default kwargs for csv.writer it will recognize that the list has commas in the string representation of the list and automatically quote it for you.

import csv
with open('filename.csv', 'w') as f:
   L = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
   fieldnames = ['index', 'name', 'lists']
   writer = csv.writer(f)
   writer.writerow(fieldnames)
   for i, row in enumerate(L):
       writer.writerow([str(i), 'name{}'.format(i), row])

If you look at filename.csv you get

index,name,lists
0,name_0,"[1, 2, 3]"
1,name_1,"[4, 5, 6]"
2,name_2,"[7, 8, 9]"

answered Mar 29, 2019 at 20:09

Skam

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Comments

Cloudy_Green · Accepted Answer · 2019-03-29 21:30:51Z

You only have 3 rows in your sheet, is that correct? If so, Pandas.DataFrame would be a great fit for this issue.

#import pandas moudle first
import pandas as pd  


#If you want to add `index` as the column name
index=[0,1,2]
name =['name 0','name 1','name 2']
#This is your original list in Python
L = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

#Using pd.DataFrame function to reformat the list into table
#Name the first column as 'index', the second column as 'name', and the last column as'lists'

table = pd.DataFrame({'index':index,
                      'name':name,
                      'lists':L})

#Write DataFrame to a comma-separated values (csv) file
table.to_csv('L.csv', index=False)

If you try to print the result, it will show like following (apologize I don't know how to embed the table properly)

<table>
  <tr>
    <td></td>
    <td>index</td>
    <td>name</td>
    <td>list</td>
  </tr>
  <tr>
    <td>0</td>
    <td>0</td>
    <td>name 1</td>
    <td>[1, 2, 3]</td>
  </tr>
  <tr>
    <td>1</td>
    <td>1</td>
    <td>name 2</td>
    <td>[4, 5, 6]</td>
  </tr>
  <tr>
    <td>1</td>
    <td>1</td>
    <td>name 3</td>
    <td>[7, 8, 9]</td>
  </tr>
</table>

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