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Nacho DP
Nacho DP

Reputation: 13

How do I duplicate CSV rows row_number times?

I am trying to use Python to generate a CSV file "distances" where I want to duplicate the rows of another file, "result" like this:

result.csv:

|ID |
|---|
| 1 |
| 2 |
| 3 |
...

distances.csv

|ID1 |ID2 |
|----|----|
| 1  | 1  |
| 1  | 2  |
| 1  | 3  |
| 2  | 1  |
| 2  | 2  |
| 2  | 3  |
...

Here is my Python code:

with open('distances.csv', 'wb') as ff:
    writer = csv.writer(ff, delimiter=";", quoting=csv.QUOTE_ALL)

    with open('result.csv', 'rb') as f:
        reader = csv.reader(f, delimiter=";", quoting=csv.QUOTE_NONE)
        reader2 = csv.reader(f, delimiter=";", quoting=csv.QUOTE_NONE)

        for row in reader:
            for row2 in reader2:
                lst = []
                lst.append(row[0])
                lst.append(row[1])
                lst.append(row2[0])
                lst.append(row2[1])

                writer.writerow([unicode(s).encode("utf-8") for s in lst])

For some reason it only duplicates the first row in result.csv

Thanks in advance!

Upvotes: 0

Views: 1612

Answers (2)

Moses Koledoye
Moses Koledoye

Reputation: 78554

You can use itertools.product to make the repetitions on column ID in distance.csv:

from itertools import product
import csv


with open('result.csv', 'r') as fin, open('distance.csv', 'w') as fout:
    reader = csv.reader(fin, delimiter=";", quoting=csv.QUOTE_NONE)
    writer = csv.writer(fout, delimiter=";", quoting=csv.QUOTE_ALL)

    # skip header
    next(reader)

    buffer_ = [row[0] for row in reader]

    writer.writerow(['ID1', 'ID2'])
    writer.writerows(i for i in product(buffer_, repeat=2))

If you need more than 2 duplications: 'ID1', 'ID2',..., 'IDn', change the repeat value in product to n

Upvotes: 2

Eugene Yarmash
Eugene Yarmash

Reputation: 150128

Since the csv.reader is an iterator over the file, you can only go through it once. Try reading the rows into a list:

with open("result.csv", "b") as f, open("distances.csv", "wb") as ff:
    reader = csv.reader(f, delimiter=";", quoting=csv.QUOTE_NONE)
    writer = csv.writer(ff, delimiter=";", quoting=csv.QUOTE_ALL)
    rows = list(reader)

    for row1 in rows:
        for row2 in rows:
            lst = row1 + row2
            writer.writerow(lst)

Upvotes: 1

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