How to split a huge csv file based on content of first column?

Question

• I have a 250MB+ huge csv file to upload
• file format is group_id, application_id, reading and data could look like

Answer 1

If the file is already sorted by group_id, you can do something like:

import csv
from itertools import groupby

for key, rows in groupby(csv.reader(open("foo.csv")),
                         lambda row: row[0]):
    with open("%s.txt" % key, "w") as output:
        for row in rows:
            output.write(",".join(row) + "\n")