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/*
* This file is part of the repicea-statistics library.
*
* Copyright (C) 2009-2019 Mathieu Fortin for Rouge-Epicea
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 3 of the License, or (at your option) any later version.
*
* This library is distributed with the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied
* warranty of MERCHANTABILITY or FITNESS FOR A
* PARTICULAR PURPOSE. See the GNU Lesser General Public
* License for more details.
*
* Please see the license at http://www.gnu.org/copyleft/lesser.html.
*/
package repicea.stats.sampling;
import java.security.InvalidParameterException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import repicea.stats.StatisticalUtility;
public class SamplingUtility {
/**
* Returns a sample from a population.
*
* @param the type of object in the population and the sample
* @param population a List of instances T standing for the population
* @param sampleSize the sample size (int)
* @param withReplacement a boolean true if sampling with replacement or false otherwise
* @return a List of instances T standing for the sample
*/
@SuppressWarnings({ "rawtypes", "unchecked" })
public static List getSample(List population, int sampleSize, boolean withReplacement) {
if (sampleSize <= 0 || sampleSize > population.size()) {
throw new InvalidParameterException("The sample size must be greater than 0 and smaller than or equal to the population size!");
}
List sampleIndex = getSampleIndex(sampleSize, population.size(), withReplacement);
List sample = new ArrayList();
for (Integer ind : sampleIndex) {
sample.add(population.get(ind));
}
return sample;
}
/**
* Returns a sample from a population drawn without replacement.
*
* @param the type of object in the population and the sample
* @param population a List of instances T standing for the population
* @param sampleSize the sample size (int)
* @return a List of instances T standing for the sample
*/
public static List getSample(List population, int sampleSize) {
return getSample(population, sampleSize, false);
}
/**
* This method returns the list of different observations and their frequency.
* @param list a population or a sample
* @return a Map with observation as keys and frequencies as values
*/
@SuppressWarnings("rawtypes")
public static Map getObservationFrequencies(Collection list) {
Map frequencyMap = new HashMap();
for (Object obj : list) {
if (!frequencyMap.containsKey(obj)) {
frequencyMap.put(obj, 0);
}
frequencyMap.put(obj, frequencyMap.get(obj) + 1);
}
return frequencyMap;
}
/**
* Return a random sample of observation indices.
*
* The theoretical observations are labeled from 0 to N-1 where N is the population size.
*
* @param sampleSize the sample size
* @param populationSize the population size
* @param withReplacement allow sampling with replacement
* @return a List of integers
*/
public static List getSampleIndex(int sampleSize, int populationSize, boolean withReplacement) {
List sampleIndex = new ArrayList();
getSampleIndex(sampleSize, populationSize, withReplacement, sampleIndex);
return sampleIndex;
}
/**
* Return a random sample of observation indices.
* The theoretical observations are labeled from 0 to N-1 where N is the population size. This
* method is equivalent to the getSampleIndex(int, int, boolean) method except that the return
* object is passed as an argument. Should be preferred in case of multithreading because it avoids
* creating a new array at each call.
*
* @param sampleSize the sample size
* @param populationSize the population size
* @param withReplacement allow sampling with replacement
* @param sampleIndex the list of randomly drawn indices
*/
public static void getSampleIndex(int sampleSize, int populationSize, boolean withReplacement, List sampleIndex) {
sampleIndex.clear();
int index;
while (sampleIndex.size() < sampleSize) {
index = (int) Math.floor(StatisticalUtility.getRandom().nextDouble() * populationSize);
if (withReplacement || !sampleIndex.contains(index)) {
sampleIndex.add(index);
}
}
}
/**
* This method returns a sample from a population drawn without replacement..
* @param population a Map instance with the population
* @param sampleSize an integer
* @return a Map instance containing the sample
*/
@SuppressWarnings({ "rawtypes", "unchecked" })
public static Map getSample(Map population, int sampleSize) {
if (sampleSize <= 0 || sampleSize > population.size()) {
throw new InvalidParameterException("The sample size must be greater than 0 and smaller than or equal to the population size!");
}
List keys = new ArrayList();
for (Object key : population.keySet()) {
keys.add(key);
}
List sampleIndex = getSampleIndex(sampleSize, population.size(), false);
Map sample = new HashMap();
for (Integer ind : sampleIndex) {
Object key = keys.get(ind);
Object value = population.get(key);
sample.put(key, value);
}
return sample;
}
}