Sorting text file by using Python

Question

I have a text file includes over than 10 million lines. Lines like that:

37024469;196672001;255.0000000000
37024469;196665001;396.0000000000
37024469;196664001;396.0000000000
37024469;196399002;85.0000000000
37024469;160507001;264.0000000000
37024469;160506001;264.0000000000

As you seen, delimiter is ";". i would like to sort this text file by using python according to the second element. I couldnt use split function. Because it causes MemoryError. how can i manage it ?

Answer 1

Don't sort 10 million lines in memory. Split this up in batches instead:

• Run 100 100k line sorts (using the file as an iterator, combined with islice() or similar to pick a batch). Write out to separate files elsewhere.

• Merge the sorted files. Here is an merge generator that you can pass 100 open files and it'll yield lines in sorted order. Write to a new file line by line:

  import operator
  
  def mergeiter(*iterables, **kwargs):
      """Given a set of sorted iterables, yield the next value in merged order
  
      Takes an optional `key` callable to compare values by.
      """
      iterables = [iter(it) for it in iterables]
      iterables = {i: [next(it), i, it] for i, it in enumerate(iterables)}
      if 'key' not in kwargs:
          key = operator.itemgetter(0)
      else:
          key = lambda item, key=kwargs['key']: key(item[0])
  
      while True:
          value, i, it = min(iterables.values(), key=key)
          yield value
          try:
              iterables[i][0] = next(it)
          except StopIteration:
              del iterables[i]
              if not iterables:
                  raise