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MALLET is a Java-based package for statistical natural language processing, document classification, clustering, topic modeling, information extraction, and other machine learning applications to text.

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/* This file is part of "MALLET" (MAchine Learning for LanguagE Toolkit).
   http://www.cs.umass.edu/~mccallum/mallet
   This software is provided under the terms of the Common Public License,
   version 1.0, as published by http://www.opensource.org.  For further
   information, see the file `LICENSE' included with this distribution. */

package cc.mallet.classify;

import java.util.HashMap;
import java.util.TreeMap;

import cc.mallet.classify.Classification;
import cc.mallet.classify.Classifier;
import cc.mallet.pipe.Pipe;
import cc.mallet.types.Instance;
import cc.mallet.types.Label;


/**
 * A Classifier that will return the most frequent class label based on a training set.
 * The Classifier needs to be trained using the MostFrequentClassAssignmentTrainer.
 * 
 * @see MostFrequentClassAssignmentTrainer
 * 
 * @author Martin Wunderlich [email protected]
*/
public class MostFrequentClassifier extends Classifier {

	TreeMap sortedLabelMap = new TreeMap();
	HashMap labels = new HashMap();
	
	/**
	 * 
	 */
	private static final long serialVersionUID = -2685212760735255652L;

	public MostFrequentClassifier(Pipe instancePipe) {
		this.instancePipe = instancePipe;
	}

    /**
     * Classify an instance using the most frequent class label.
     * 
     * @param Instance to be classified. Data field must be a FeatureVector.
     * @return Classification containing the labeling of the instance.
     */
	@Override
	public Classification classify(Instance instance) {
		String mostFrequentLabelStr = this.sortedLabelMap.firstEntry().getKey();
		Label mostFrequentLabel = this.labels.get(mostFrequentLabelStr);
		Classification mostFrequentClassification = new Classification(instance, this, mostFrequentLabel);
		
		return mostFrequentClassification;
	}

	public void addTargetLabel(Label label) {
		String labelEntry = (String) label.getEntry();
		
		if(! this.labels.containsKey(labelEntry) ) {
			this.sortedLabelMap.put(labelEntry, new Integer(1));
			this.labels.put(labelEntry, label);
		}
		else {
			Integer oldCount = this.sortedLabelMap.get(labelEntry);
			Integer newCount = oldCount + 1;
			this.sortedLabelMap.put(labelEntry, newCount);
			this.labels.put(labelEntry, label);
		}
	}
}