Pandas: Merging Sorted Dataframes

[RockRoll]

Hi,

I have a large (Nx4, >10GB) array that I need to sort based on col.2.

I am reading my data in chunks and sorting using Pandas. But I am unable to combine the sorted chunks to give me a final large Nx4 array that is sorted on Col.2. Here is what I have tried yet:

chunks = pd.read_csv(ifile[0], chunksize=50000, skiprows=0,
                     names=['col-1', 'col-2', 'col-3', 'col-4'])

for df in chunks:
    df = df.sort_values(by='col-2', kind='mergesort') # sorted chunks
    print(df)

[SioSio]

The process when reading the file divided is as follows.

import pandas as pd
df = None
for tmp in  pd.read_csv(ifile[0], chunksize=50000, names=['col-1', 'col-2', 'col-3', 'col-4']):
    if df is None:
        df = tmp
    else:
        df = df.append(tmp, ignore_index=True)

df_s = df.sort_values(by='col-2', kind='mergesort')
print(df_s)

[madankarmukta]

Follow standalone syntaxt for sort_values.

Thanks