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/*
* Copyright 2015 The Android Open Source Project
*
* 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 tests.util;
public class SummaryStatistics {
/** The number of values seen. */
private int numValues;
/** Sum of the values. */
private double sum;
/** Use the first value to shift all values to it when computing variance, as it improves
* numerical stability. Note variance is invariant to shifting. */
private Double firstValue = null;
/** Sum of the squares of the values added, shifted according to the first value. */
private double shiftedSquaresSum;
public SummaryStatistics() {
}
private double square(double value) {
return value * value;
}
/** Add a new value to the values seen. */
public void add(double value) {
if (firstValue == null) {
firstValue = new Double(value);
}
sum += value;
shiftedSquaresSum += square(value - firstValue);
numValues++;
}
/** Mean of the values seen. */
public double mean() {
return sum / numValues;
}
/** Variance of the values seen. */
public double var() {
double shiftedMean = (sum - numValues * firstValue) / numValues;
return (shiftedSquaresSum / numValues) - square(shiftedMean);
}
/** Standard deviation of the values seen. */
public double stddev() {
return Math.sqrt(var());
}
/** Coefficient of variation of the values seen. */
public double coeffVar() {
return stddev() / mean();
}
public String toString() {
StringBuilder sb = new StringBuilder("SummaryStatistics{");
sb.append("n=");
sb.append(numValues);
sb.append(",mean=");
sb.append(mean());
sb.append(",var=");
sb.append(var());
sb.append(",stddev=");
sb.append(stddev());
sb.append(",coeffVar=");
sb.append(coeffVar());
sb.append('}');
return sb.toString();
}
}
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