CODEWITHSUNDEEP
pythonarrayscsvfile-writing
DGraham
DGraham

Reputation: 715

Writing arrays to a csv in columns

I have been trying to solve a basic problem (and have been Python 2.7, and have got no where. I have a csv file with column headings such as:

a,b,c
1,2,3
1,2,3
1,2,3

This is saved as test1.csv

I have managed to take each column and pass them into an array, so each column heading is at the start, followed by the data. How would I then write this back into a new csv file with the same order and structure?

import csv

f = open('test1.csv','rb')

reader = csv.reader(f)
headers = reader.next()
print headers

column = {}
for h in headers:
    column[h] = []  

for row in reader:
    for h,v in zip(headers,row):
    column[h].append(v)

Upvotes: 2

Views: 4592

Answers (1)

martineau
martineau

Reputation: 123531

You could write (and read) the data like this, which uses a defaultdict instead of a plain dictionary to simplify its construction:

from collections import defaultdict
import csv

with open('test1.csv', 'rb') as f:
    reader = csv.reader(f)
    header = next(reader)
    columns = defaultdict(list)
    for row in reader:
        for col,value in zip(header, row):
            columns[col].append(value)
    num_rows = len(columns[header[0]])

# now write data back out in same order

with open('test2.csv', 'wb') as f:
    writer = csv.writer(f)
    writer.writerow(header)
    writer.writerows(
        tuple(columns[col][row] for col in header) for row in xrange(num_rows))

Upvotes: 2

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