| /* |
| * Copyright (C) 2014 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 com.android.cts.util; |
| |
| |
| import java.util.ArrayList; |
| import java.util.Collection; |
| import java.util.Collections; |
| import java.util.List; |
| import java.util.concurrent.TimeUnit; |
| |
| /** |
| * Set of static helper methods for CTS tests. |
| */ |
| public class StatisticsUtils { |
| |
| |
| /** |
| * Private constructor for static class. |
| */ |
| private StatisticsUtils() {} |
| |
| /** |
| * Get the value of the 95th percentile using nearest rank algorithm. |
| * |
| * @throws IllegalArgumentException if the collection is null or empty |
| */ |
| public static <TValue extends Comparable<? super TValue>> TValue get95PercentileValue( |
| Collection<TValue> collection) { |
| validateCollection(collection); |
| |
| List<TValue> arrayCopy = new ArrayList<TValue>(collection); |
| Collections.sort(arrayCopy); |
| |
| // zero-based array index |
| int arrayIndex = (int) Math.round(arrayCopy.size() * 0.95 + .5) - 1; |
| |
| return arrayCopy.get(arrayIndex); |
| } |
| |
| /** |
| * Calculate the mean of a collection. |
| * |
| * @throws IllegalArgumentException if the collection is null or empty |
| */ |
| public static <TValue extends Number> double getMean(Collection<TValue> collection) { |
| validateCollection(collection); |
| |
| double sum = 0.0; |
| for(TValue value : collection) { |
| sum += value.doubleValue(); |
| } |
| return sum / collection.size(); |
| } |
| |
| /** |
| * Calculate the bias-corrected sample variance of a collection. |
| * |
| * @throws IllegalArgumentException if the collection is null or empty |
| */ |
| public static <TValue extends Number> double getVariance(Collection<TValue> collection) { |
| validateCollection(collection); |
| |
| double mean = getMean(collection); |
| ArrayList<Double> squaredDiffs = new ArrayList<Double>(); |
| for(TValue value : collection) { |
| double difference = mean - value.doubleValue(); |
| squaredDiffs.add(Math.pow(difference, 2)); |
| } |
| |
| double sum = 0.0; |
| for (Double value : squaredDiffs) { |
| sum += value; |
| } |
| return sum / (squaredDiffs.size() - 1); |
| } |
| |
| /** |
| * Calculate the bias-corrected standard deviation of a collection. |
| * |
| * @throws IllegalArgumentException if the collection is null or empty |
| */ |
| public static <TValue extends Number> double getStandardDeviation( |
| Collection<TValue> collection) { |
| return Math.sqrt(getVariance(collection)); |
| } |
| |
| /** |
| * Validate that a collection is not null or empty. |
| * |
| * @throws IllegalStateException if collection is null or empty. |
| */ |
| private static <T> void validateCollection(Collection<T> collection) { |
| if(collection == null || collection.size() == 0) { |
| throw new IllegalStateException("Collection cannot be null or empty"); |
| } |
| } |
| |
| } |