FixedStreamFeatureStatistics.java

/**
 * Copyright 2013-2015 Pierre Merienne
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * 		http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.github.pmerienne.trident.ml.stats;

import java.io.Serializable;

public class FixedStreamFeatureStatistics implements StreamFeatureStatistics, Serializable {

	private static final long serialVersionUID = -7406184811401750690L;

	private long count = 0L;
	private double mean = 0.0;
	private double m2 = 0.0;

	public void update(double feature) {
		this.count = this.count + 1;
		double delta = feature - this.mean;
		this.mean = this.mean + delta / this.count;
		this.m2 = this.m2 + delta * (feature - this.mean);
	}

	@Override
	public Long getCount() {
		return count;
	}

	@Override
	public Double getMean() {
		return mean;
	}

	@Override
	public Double getVariance() {
		return m2 / (count - 1);
	}

	@Override
	public Double getStdDev() {
		return Math.sqrt(this.getVariance());
	}

	@Override
	public String toString() {
		return "SimpleStreamFeatureStatistics [m2=" + m2 + ", count=" + count + ", mean=" + mean + ", variance=" + getVariance() + ", stdDev=" + getStdDev()
				+ "]";
	}

}