MovingAverageCalculator.java

/*******************************************************************************
 * Copyright (c) 2012 jnect.org.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     Eugen Neufeld - initial API and implementation
 *     Istvan Rath - IncQuery-specific additions
 *******************************************************************************/
package bodymodel;

import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.Queue;

import org.eclipse.xtext.xbase.lib.Pure;
/**
 * This class helps to calculate a moving average, this way the data can be cleaned.
 * @author Philip Achenbach
 * @author Eugen Neufeld
 * 
 * Originally found in http://code.google.com/a/eclipselabs.org/p/jnect/
 * 
 * XXX foreign IP
 * 
 * @author istvanrath - modifications to allow factory-style operation so that it can be meaningfully used from IncQuery queries
 */

public class MovingAverageCalculator {

	private final Queue<Float> window = new LinkedList<Float>();
	private final int numPeriods;
	private float sum;
	
	/**
	 * instantiate the {@link MovingAverageCalculator} with a number of periods to build the average over
	 * @param numPeriods - number of values to build the average over
	 */
	public MovingAverageCalculator(int numPeriods) {
		this.numPeriods = numPeriods;
	}
	/**
	 * add a value to the moving average, if the number of periods is exceeded, then the oldest value is removed.  
	 * @param num - the value to add to the moving average
	 */
	//@Pure
	public MovingAverageCalculator addValue(float num) {
		sum += num;
		window.add(num);
		if (window.size() > numPeriods) {
			sum -= window.remove();
		}
		return this;
	}
	/**
	 * get the current moving average
	 * @return - current value of the moving average
	 */
	//@Pure
	public float getMovingAvg() {
		return (window.size() == 0) ? 0 : sum / window.size();
	}
	
	/* istvanrath's modifications below */
	
	static Map<String, MovingAverageCalculator> calculators = new HashMap<String, MovingAverageCalculator>();
	
	public static int periodLength = 10;
	
	@Pure
	public static MovingAverageCalculator getCalculator(String key) {
		if (calculators.containsKey(key)) {
			return calculators.get(key); 
		} else {
			MovingAverageCalculator mac = new MovingAverageCalculator(periodLength);
			calculators.put(key, mac);
			return mac;
		}
	}
	
}