Removing duplicate rows from a csv file using a python script

Question

Goal

I have downloaded a CSV file from hotmail, but it has a lot of duplicates in it. These duplicates are complete copies and I don\'t know why my

Answer 1

I know this is long settled, but I have had a closely related problem whereby I was to remove duplicates based on one column. The input csv file was quite large to be opened on my pc by MS Excel/Libre Office Calc/Google Sheets; 147MB with about 2.5 million records. Since I did not want to install a whole external library for such a simple thing, I wrote the python script below to do the job in less than 5 minutes. I didn't focus on optimization, but I believe it can be optimized to run faster and more efficient for even bigger files. The algorithm is similar to @IcyFlame above, except that I am removing duplicates based on a column ('CCC') instead of whole row/line.

import csv

with open('results.csv', 'r') as infile, open('unique_ccc.csv', 'a') as outfile:
    # this list will hold unique ccc numbers,
    ccc_numbers = []
    # read input file into a dictionary, there were some null bytes in the infile
    results = csv.DictReader(infile)
    writer = csv.writer(outfile)

    # write column headers to output file
    writer.writerow(
        ['ID', 'CCC', 'MFLCode', 'DateCollected', 'DateTested', 'Result', 'Justification']
    )
    for result in results:
        ccc_number = result.get('CCC')
        # if value already exists in the list, skip writing it whole row to output file
        if ccc_number in ccc_numbers:
            continue
        writer.writerow([
            result.get('ID'),
            ccc_number,
            result.get('MFLCode'),
            result.get('datecollected'),
            result.get('DateTested'),
            result.get('Result'),
            result.get('Justification')
        ])

        # add the value to the list to so as to be skipped subsequently
        ccc_numbers.append(ccc_number)