/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.mahout.cf.taste.impl.common;
import org.apache.mahout.cf.taste.impl.TasteTestCase;
import org.apache.mahout.common.RandomUtils;
import org.junit.Test;
import java.util.Random;
public final class RunningAverageAndStdDevTest extends TasteTestCase {
private static final double SMALL_EPSILON = 1.0;
@Test
public void testFull() {
RunningAverageAndStdDev average = new FullRunningAverageAndStdDev();
assertEquals(0, average.getCount());
assertTrue(Double.isNaN(average.getAverage()));
assertTrue(Double.isNaN(average.getStandardDeviation()));
average.addDatum(6.0);
assertEquals(1, average.getCount());
assertEquals(6.0, average.getAverage(), EPSILON);
assertTrue(Double.isNaN(average.getStandardDeviation()));
average.addDatum(6.0);
assertEquals(2, average.getCount());
assertEquals(6.0, average.getAverage(), EPSILON);
assertEquals(0.0, average.getStandardDeviation(), EPSILON);
average.removeDatum(6.0);
assertEquals(1, average.getCount());
assertEquals(6.0, average.getAverage(), EPSILON);
assertTrue(Double.isNaN(average.getStandardDeviation()));
average.addDatum(-4.0);
assertEquals(2, average.getCount());
assertEquals(1.0, average.getAverage(), EPSILON);
assertEquals(5.0 * 1.4142135623730951, average.getStandardDeviation(), EPSILON);
average.removeDatum(4.0);
assertEquals(1, average.getCount());
assertEquals(-2.0, average.getAverage(), EPSILON);
assertTrue(Double.isNaN(average.getStandardDeviation()));
}
@Test
public void testFullBig() {
RunningAverageAndStdDev average = new FullRunningAverageAndStdDev();
Random r = RandomUtils.getRandom();
for (int i = 0; i < 100000; i++) {
average.addDatum(r.nextDouble() * 1000.0);
}
assertEquals(500.0, average.getAverage(), SMALL_EPSILON);
assertEquals(1000.0 / Math.sqrt(12.0), average.getStandardDeviation(), SMALL_EPSILON);
}
@Test
public void testStddev() {
RunningAverageAndStdDev runningAverage = new FullRunningAverageAndStdDev();
assertEquals(0, runningAverage.getCount());
assertTrue(Double.isNaN(runningAverage.getAverage()));
runningAverage.addDatum(1.0);
assertEquals(1, runningAverage.getCount());
assertEquals(1.0, runningAverage.getAverage(), EPSILON);
assertTrue(Double.isNaN(runningAverage.getStandardDeviation()));
runningAverage.addDatum(1.0);
assertEquals(2, runningAverage.getCount());
assertEquals(1.0, runningAverage.getAverage(), EPSILON);
assertEquals(0.0, runningAverage.getStandardDeviation(), EPSILON);
runningAverage.addDatum(7.0);
assertEquals(3, runningAverage.getCount());
assertEquals(3.0, runningAverage.getAverage(), EPSILON);
assertEquals(3.464101552963257, runningAverage.getStandardDeviation(), EPSILON);
runningAverage.addDatum(5.0);
assertEquals(4, runningAverage.getCount());
assertEquals(3.5, runningAverage.getAverage(), EPSILON);
assertEquals(3.0, runningAverage.getStandardDeviation(), EPSILON);
}
}