SentencesBlocks.cc

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// -*- C++ -*-

// PLearn (A C++ Machine Learning Library)
// Copyright (C) 1998 Pascal Vincent
// Copyright (C) 1999-2001 Pascal Vincent, Yoshua Bengio, Rejean Ducharme and University of Montreal
// Copyright (C) 2002 Pascal Vincent, Julien Keable, Xavier Saint-Mleux
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
// 
//  1. Redistributions of source code must retain the above copyright
//     notice, this list of conditions and the following disclaimer.
// 
//  2. Redistributions in binary form must reproduce the above copyright
//     notice, this list of conditions and the following disclaimer in the
//     documentation and/or other materials provided with the distribution.
// 
//  3. The name of the authors may not be used to endorse or promote
//     products derived from this software without specific prior written
//     permission.
// 
// THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
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// This file is part of the PLearn library. For more information on the PLearn
// library, go to the PLearn Web site at www.plearn.org


/* *******************************************************      
   * $Id: SentencesBlocks.cc,v 1.3 2004/02/20 21:14:44 chrish42 Exp $
   ******************************************************* */

#include "SentencesBlocks.h"

namespace PLearn {
using namespace std;

SentencesBlocks::SentencesBlocks(int n_blocks, VMat d, Vec separator)
  : TVec<VMat>(n_blocks)
{
  if (n_blocks==1) 
  {
    (*this)[0]=d;
    return;
  }
  int total_size = d->length();
  if (total_size < n_blocks * 2)
    PLERROR("SentencesBlocks: can't have blocks of size < 2 in average");
  Vec v(d->width());
  int b=0;
  int previous_previous_block=0,previous_beginning_of_block = 0, previous_beginning_of_sentence=0;
  int next_target = (int)(total_size / (real)n_blocks);
  for (int i=0;i<total_size && b<n_blocks-1;i++)
  {
    d->getRow(i,v);
    if (v==separator)
    {
      if (i>=next_target)
      {
        int cut=0;
        if (i-next_target < next_target-previous_beginning_of_sentence ||
            previous_beginning_of_sentence < previous_beginning_of_block)
          cut=i+1;
        else
        {
          cut=previous_beginning_of_sentence;
          previous_beginning_of_sentence = i+1;
        }
        (*this)[b++] = d.subMatRows(previous_beginning_of_block,
                                    cut-previous_beginning_of_block);
        previous_previous_block = previous_beginning_of_block;
        previous_beginning_of_block=cut;
        if (b<n_blocks)
        {
          if (b>n_blocks-3)
            next_target = (int)((total_size - cut) / (real)(n_blocks-b));
          else
            next_target = (int)(total_size * (real)(b+1.0) / n_blocks);
        }
      }
      else
        previous_beginning_of_sentence=i+1;
    }
  }
  if (b==n_blocks-1)
    (*this)[b++] = d.subMatRows(previous_beginning_of_block,
                                total_size-previous_beginning_of_block);
  if (b<n_blocks-1) // we have to backtrack, split previous block in two
  {
    if (b<n_blocks-2)
      PLERROR("SentencesBlocks: blocks are too small!");
    if (previous_beginning_of_sentence<previous_beginning_of_block)
      PLERROR("SentencesBlocks: Blocks are too small!");
    int cut = previous_beginning_of_sentence;
    (*this)[b++] = d.subMatRows(previous_beginning_of_block,
                                cut-previous_beginning_of_block);
    previous_beginning_of_block=cut;
    (*this)[b++] = d.subMatRows(previous_beginning_of_block,
                                total_size-previous_beginning_of_block);
  }
}

} // end of namespace PLearn

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