package de.spieleck.app.cngram ;
/* Please see the license information in the header below. */
/*
NGramJ - n-gram based text classification
Copyright (C) 2001- Frank S. Nestel (frank at spieleck.de)
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published
by the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program (lesser.txt); if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
import java.util.Iterator ;
/**
* This metric is based on a loose interpretation of the Chi^2 formula.
* @author frank nestel
* @author $Author: nestefan $
* @version $Revision: 2 $ $Date: 2006-03-27 23:00:21 +0200 (Mo, 27 Mrz 2006) $ $Author: nestefan $
*/
public class C2aMetric
implements NGramMetric
{
public double diff( NGramProfile p1 , NGramProfile p2 )
{
double sum = 0.0 ;
int norm1 = p1.getNormalization() ;
int norm2 = p2.getNormalization() ;
// Treat all NGrams contained in p1;
Iterator i = p1.getSorted() ;
while ( i.hasNext() )
{
NGram ng1 = (NGram)i.next() ;
NGram ng2 = p2.get( ng1 ) ;
double c1 = (double)ng1.getCount() / norm1 ;
if ( ng2 != null )
{
double c2 = (double)ng2.getCount() / norm2 ;
sum += ( c1 - c2 ) * ( c1 - c2 ) / ( c1 + c2 ) ;
}
else
{
sum += c1 ;
}
}
// Treat NGrams contained ONLY in p2
i = p2.getSorted() ;
while ( i.hasNext() )
{
NGram ng2 = (NGram)i.next() ;
if ( p1.get( ng2 ) == null )
{
double c2 = (double)ng2.getCount() / norm2 ;
sum += c2 ;
}
}
return sum ;
}
}