Write a 2d array to a csv file with delimiter [duplicate]

Question

As the title says, I want to write a 2D array to a csv file with delimiter ',' using python. My array looks like this (ndarray):

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

and I want the output to look like:

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

with open('./data/positive.csv','wb') as myfile:
  wr = csv.writer(myfile) #, quoting=csv.QUOTE_ALL)
  wr.writerow(a)

How do I accomplish this?

I already have tried the solution but it doesn't work since I misplaced an 's' in my 'row' and it makes my array write to a single row instead of multiple rows.

Answer 1

Use csv module by import csv also take a note you might need either writerow() or writerows().

What's the difference you may ask?

writerow takes an iterable of cells to write:

writerow([1,2,2])
->
1,2,2

writerows takes an iterable of iterables of cells to write:

writerows([[1,2,3],
           [4,5,6],
           [6,7,8]])
->
1,2,3
4,5,6
6,7,8

Which can be ofcourse be given as a variable. Like

a = [[1,2,3],[4,5,6],[6,7,8]]
writerows(a)

Conclusion writerow takes 1-dimensional data (one row), and writerows takes 2-dimensional data (multiple rows).

Program for you:

import csv

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

with open("new_file.csv","w+") as my_csv:
    csvWriter = csv.writer(my_csv,delimiter=',')
    csvWriter.writerows(a)

Note open() takes two arguments here the file to be written and the mode.

What is a mode you may ask?

It specifies how the file should be opened. In my case w+ means open file my_file.csv if it exists if it doesn't then fine create a new one and write.

There are several modes choose one. Note: w+ overwrites everytime you use it. That is old data in file will be overwritten so if you want to just append use a. Take a look at this for more details on modes.File modes