Python, transposing a list and writing to a CSV file

Question

I need to write into a csv file using python and each iterator item should start in a new line. So delimiter I am using is "\n". After each list has been written,next list should write from next cell. like below:

 lol = [[1,2,3],[4,5,6]]

The csv will be like:

1 4
2 5
3 6

What I have tried:

file = open("test.csv", "wb")
fileWriter = csv.writer(file , delimiter='\n',quotechar='|', quoting=csv.QUOTE_MINIMAL)
spamWriter.writerow([1,2,3])
spamWriter = csv.writer(file , delimiter=',',quotechar='|', quoting=csv.QUOTE_MINIMAL)
spamWriter.writerow([4,5,6])
file.close()

Which results like below:

Using csv module how can I get output like below:

 1 4 
 2 5
 3 6

here space means comma in a csv file.

Thanks.

score 13 · Accepted Answer · answered May 13 '12 at 18:32

Without using zip, you could do this:

import csv

lol = [[1,2,3],[4,5,6],[7,8,9]]
item_length = len(lol[0])

with open('test.csv', 'wb') as test_file:
  file_writer = csv.writer(test_file)
  for i in range(item_length):
    file_writer.writerow([x[i] for x in lol])

This will output into test.csv:

1,4,7
2,5,8
3,6,9

Kimvais · Answer 2 · 2012-05-13T18:22:39.280

11

first transpose your input by using zip()

>>> zip(*lol)
[(1, 4), (2, 5), (3, 6)]

and after that just pass it to csw.writer e.g.

with open("test.csv", "wb") as f:
    fileWriter = csv.writer(f, delimiter=',',quotechar='|', quoting=csv.QUOTE_MINIMAL)
    for row in zip(*lol):
        fileWriter.writerow(row)

... which results to:

$ cat test.csv 
1,4
2,5
3,6

edited May 13 '12 at 18:22

answered May 13 '12 at 17:55

Kimvais

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it writes with [ and ] character – May 13 '12 at 18:08
I think you should just change the write attribute to `w` instead of `wb`, and then this answer will work perfectly.. – Vishal Jul 07 '20 at 08:58

score 4 · Answer 3 · answered Feb 22 '18 at 12:50

If you are using Python3 you need to open files in text format "wt", more over csv has writerows that can be used to write everything at once. here is an example:

data=[("test", "value1", "value2"), ("test2", "value3", "value4")]
with open('my.csv','wt') as out:
   csv_out=csv.writer(out)
   csv_out.writerows(data)

I've just noticed that the question ask how to transform the list, that is a separate step and here is how I would do it:

lol = [[1,2,3],[4,5,6]]
data = zip(lol[0],lol[1])

Python, transposing a list and writing to a CSV file

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