Load pandas dataframe with chunksize determined by column variable

If you iterate through the csv file line by line, you can yield chunks with a generator dependent on any column.

Working example:

import pandas as pd

def iter_chunk_by_id(file):
    csv_reader = pd.read_csv(file, iterator=True, chunksize=1, header=None)
    first_chunk = csv_reader.get_chunk()
    id = first_chunk.iloc[0,0]
    chunk = pd.DataFrame(first_chunk)
    for l in csv_reader:
        if id == l.iloc[0,0]:
            id = l.iloc[0,0]
            chunk = chunk.append(l)
            continue
        id = l.iloc[0,0]
        yield chunk
        chunk = pd.DataFrame(l)
    yield chunk

## data.csv ##
# 1, foo, bla
# 1, off, aff
# 2, roo, laa
# 3, asd, fds
# 3, qwe, tre
# 3, tre, yxc   

chunk_iter = iter_chunk_by_id("data.csv")

for chunk in chunk_iter:
    print(chunk)
    print("_____")

Output:

   0     1     2
0  1   foo   bla
1  1   off   aff
_____
   0     1     2
2  2   roo   laa
3  2   jkl   xds
_____
   0     1     2
4  3   asd   fds
5  3   qwe   tre
6  3   tre   yxc
_____

I built on the answer provided by @elcombato to take any chunk size. I actually had a similar use case and processing each line one by one made my program unbearably slow

def iter_chunk_by_id(file_name, chunk_size=10000):
"""generator to read the csv in chunks of user_id records. Each next call of generator will give a df for a user"""

csv_reader = pd.read_csv(file_name, compression='gzip', iterator=True, chunksize=chunk_size, header=0, error_bad_lines=False)
chunk = pd.DataFrame()
for l in csv_reader:
    l[['id', 'everything_else']] = l[
        'col_name'].str.split('|', 1, expand=True)
    hits = l['id'].astype(float).diff().dropna().nonzero()[0]
    if not len(hits):
        # if all ids are same
        chunk = chunk.append(l[['col_name']])
    else:
        start = 0
        for i in range(len(hits)):
            new_id = hits[i]+1
            chunk = chunk.append(l[['col_name']].iloc[start:new_id, :])
            yield chunk
            chunk = pd.DataFrame()
            start = new_id
        chunk = l[['col_name']].iloc[start:, :]

yield chunk