Writing large Pandas Dataframes to CSV file in chunks

Question

How do I write out a large data file to a CSV file in chunks?

I have a set of large data files (1M rows x 20 cols). However, only 5 or so columns of that data is of

Answer 1

Solution:

header = True
for chunk in chunks:

    chunk.to_csv(os.path.join(folder, new_folder, "new_file_" + filename),
        header=header, cols=[['TIME','STUFF']], mode='a')

    header = False

Notes:

• The mode='a' tells pandas to append.
• We only write a column header on the first chunk.

Answer 2

Check out the chunksize argument in the to_csv method. Here are the docs.

Writing to file would look like:

df.to_csv("path/to/save/file.csv", chunksize=1000, cols=['TIME','STUFF'])

Answer 3

Why don't you only read the columns of interest and then save it?

file_in = os.path.join(folder, filename)
file_out = os.path.join(folder, new_folder, 'new_file' + filename)

df = pd.read_csv(file_in, sep='\t', skiprows=(0, 1, 2), header=0, names=['TIME', 'STUFF'])
df.to_csv(file_out)