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Pandas: Merging Sorted Dataframes

P: 10
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:

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  1. chunks = pd.read_csv(ifile[0], chunksize=50000, skiprows=0,
  2.                      names=['col-1', 'col-2', 'col-3', 'col-4'])
  3.  
  4. for df in chunks:
  5.     df = df.sort_values(by='col-2', kind='mergesort') # sorted chunks
  6.     print(df)
Aug 12 '20 #1
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2 Replies

100+
P: 163
The process when reading the file divided is as follows.
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  1. import pandas as pd
  2. df = None
  3. for tmp in  pd.read_csv(ifile[0], chunksize=50000, names=['col-1', 'col-2', 'col-3', 'col-4']):
  4.     if df is None:
  5.         df = tmp
  6.     else:
  7.         df = df.append(tmp, ignore_index=True)
  8.  
  9. df_s = df.sort_values(by='col-2', kind='mergesort')
  10. print(df_s)
Aug 18 '20 #2

100+
P: 305
Follow standalone syntaxt for sort_values.

Thanks
Aug 26 '20 #3

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