PairBIDE.java

package ca.pfv.spmf.algorithms.sequentialpatterns.BIDE_and_prefixspan_with_strings;
/* This file is copyright (c) 2008-2013 Philippe Fournier-Viger
* 
* This file is part of the SPMF DATA MINING SOFTWARE
* (http://www.philippe-fournier-viger.com/spmf).
* 
* SPMF is free software: you can redistribute it and/or modify it under the
* terms of the GNU General Public License as published by the Free Software
* Foundation, either version 3 of the License, or (at your option) any later
* version.
* 
* SPMF 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 General Public License along with
* SPMF. If not, see <http://www.gnu.org/licenses/>.
*/

import java.util.HashSet;
import java.util.Set;

/**
 * This class, used by the BIDE algorithm, represents
 * an (1) item  
 * (2)  a boolean indicating if the item is contained in an itemset that was cut at left or not (a postfix). 
 * (3) a boolean indicating if the item is contained in an itemset that was cut at right or not (a prefix). 
 * and (4) the sequence IDs containing this item.
 * <br/><br/>
 * This class extends the class Pair used by PrefixSpan. It is is used by BIDE+ to
 * count the support of items.

@see Pair
@see AlgoBIDEPlus_withStrings
* @author Philippe Fournier-Viger
 */
class PairBIDE extends Pair{
	
	/** indicate if this represents the item appearing 
		// in an itemset that is cut at the right or not (a prefix) */
	private final boolean prefix; 
	
	/** List of the its of all the patterns that contains this one. */
	private Set<Integer> sequencesID = new HashSet<Integer>();
	
	/**
	 * Constructor
	 * @param postfix indicate if this is the case of an item appearing
	 *  in an itemset that is cut at the left because of a projection
	 *  @param prefix indicate if this is the case of an item appearing
	 *  in an itemset that is cut at the right because of a projection
	 * @param item the item
	 */
	PairBIDE(boolean prefix, boolean postfix, String item){
		super(postfix, item);
		this.prefix  = prefix;
	}
	
	/**
	 * Check if two pairs are equal (same item and both appears in a postfix or not and prefix or not).
	 * @return true if equals.
	 */
	public boolean equals(Object object){
		PairBIDE paire = (PairBIDE) object;
		if((paire.postfix == this.postfix) 
				&& (paire.prefix == this.prefix)
				&& (paire.item.equals(this.item))){
			return true;
		}
		return false;
	}
	
	/**
	 * Method to calculate an hashcode (because pairs are stored in a map).
	 */
	public int hashCode()
	{// Ex: 127333,P,X,1  127333,N,Z,2
		// transform it into a string
		StringBuilder r = new StringBuilder();
		r.append((postfix ? 'P' : 'N')); // the letters here have no meanings. they are just used for the hashcode
		r.append((prefix ? 'X' : 'Z')); // the letters here have no meanings. they are just used for the hashcode
		r.append(item);
		// then use the hashcode method from the string class
		return r.toString().hashCode();
	}
	
	/**
	 * Check if this is the case of the item appearing in a prefix
	 * @return true if this is the case.
	 */
	public boolean isPrefix() {
		return prefix;
	}
}