How can I split a large file csv file (7GB) in Python

Question

I have a 7GB csv file which I'd like to split into smaller chunks, so it is readable and faster for analysis in Python on a notebook. I would like to grab a small set from it, maybe 250MB, so how can I do this?

Answer 1

You don't need Python to split a csv file. Using your shell:

$ split -l 100 data.csv

Would split data.csv in chunks of 100 lines.

Answer 2

I had to do a similar task, and used the pandas package:

for i,chunk in enumerate(pd.read_csv('bigfile.csv', chunksize=500000)):
    chunk.to_csv('chunk{}.csv'.format(i), index=False)

Answer 3

Here is a little python script I used to split a file data.csv into several CSV part files. The number of part files can be controlled with chunk_size (number of lines per part file).

The header line (column names) of the original file is copied into every part CSV file.

It works for big files because it reads one line at a time with readline() instead of loading the complete file into memory at once.

#!/usr/bin/env python3

def main():
    chunk_size = 9998  # lines

    def write_chunk(part, lines):
        with open('data_part_'+ str(part) +'.csv', 'w') as f_out:
            f_out.write(header)
            f_out.writelines(lines)

    with open('data.csv', 'r') as f:
        count = 0
        header = f.readline()
        lines = []
        for line in f:
            count += 1
            lines.append(line)
            if count % chunk_size == 0:
                write_chunk(count // chunk_size, lines)
                lines = []
        # write remainder
        if len(lines) > 0:
            write_chunk((count // chunk_size) + 1, lines)

if __name__ == '__main__':
    main()