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/*
* Copyright 2013 Brian Tjaden
*
* This file is part of Rockhopper.
*
* Rockhopper is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* any later version.
*
* Rockhopper is distributed in 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* (in the file gpl.txt) along with Rockhopper.
* If not, see <http://www.gnu.org/licenses/>.
*/
import java.util.ArrayList;
import java.util.Random;
import java.util.Iterator;
public class Misc {
/*************************************************
********** PRIVATE CLASS VARIABLES **********
*************************************************/
private static Random rand; // Random number generator
/***********************************************
********** PUBLIC STATIC METHODS **********
***********************************************/
/**
* Return the element in the ArrayList corresponding to
* the specified order statistic.
*/
public static long select_Long(ArrayList<Long> a, int orderStatistic) {
return select_Long(a, 0, a.size()-1, orderStatistic);
}
/**
* Return the element in the ArrayList corresponding to
* the specified order statistic.
*/
public static double select_Double(ArrayList<Double> a, int orderStatistic) {
return select_Double(a, 0, a.size()-1, orderStatistic);
}
/**
* Returns the correlation coefficient of two ArrayLists.
*/
public static double correlation(ArrayList<Long> x, ArrayList<Long> y) {
if (x.size() != y.size()) return 0.0; // Lists have different lengths
double meanX = mean(x);
double meanY = mean(y);
double sumXY = 0.0;
double sumXX = 0.0;
double sumYY = 0.0;
for (int i=0; i<x.size(); i++) {
sumXY += (x.get(i) - meanX) * (y.get(i) - meanY);
sumXX += (x.get(i) - meanX) * (x.get(i) - meanX);
sumYY += (y.get(i) - meanY) * (y.get(i) - meanY);
}
if ((sumXX == 0.0) || (sumYY == 0.0)) return 0.0;
return sumXY / (Math.sqrt(sumXX) * Math.sqrt(sumYY));
}
/**
* Returns the mean of an ArrayList.
*/
public static double mean(ArrayList<Long> a) {
double sum = 0;
for (Iterator<Long> iter = a.iterator(); iter.hasNext(); )
sum += iter.next();
return sum / a.size();
}
/************************************************
********** PRIVATE STATIC METHODS **********
************************************************/
/**
* Return the element in the ArrayList corresponding to
* the specified order statistic.
*/
private static long select_Long(ArrayList<Long> a, int lo, int hi, int orderStatistic) {
if (lo >= hi) {
if (a.size() == 0) return 0;
return a.get(lo);
}
int p = partition(a, lo, hi);
if (orderStatistic == p-lo+1) return a.get(p);
else if (orderStatistic < p-lo+1) return select_Long(a, lo, p-1, orderStatistic);
else return select_Long(a, p+1, hi, orderStatistic-(p-lo+1));
}
/**
* Partitions "a" around random pivot element.
* Returns the index of the pivot.
*/
private static int partition(ArrayList<Long> a, int lo, int hi) {
if (rand == null) rand = new Random();
swap(a, rand.nextInt(hi-lo+1)+lo, hi); // Choose pivot randomly and place at end of "a"
long x = a.get(hi);
int i = lo-1;
for (int j=lo; j<hi; j++) {
if (a.get(j) <= x) {
i++;
swap(a, i, j);
}
}
swap(a, i+1, hi);
return i+1;
}
/**
* Return the element in the ArrayList corresponding to
* the specified order statistic.
*/
private static double select_Double(ArrayList<Double> a, int lo, int hi, int orderStatistic) {
if (lo == hi) return a.get(lo);
int p = partitionDouble(a, lo, hi);
if (orderStatistic == p-lo+1) return a.get(p);
else if (orderStatistic < p-lo+1) return select_Double(a, lo, p-1, orderStatistic);
else return select_Double(a, p+1, hi, orderStatistic-(p-lo+1));
}
/**
* Partitions "a" around random pivot element.
* Returns the index of the pivot.
*/
private static int partitionDouble(ArrayList<Double> a, int lo, int hi) {
if (rand == null) rand = new Random();
swap(a, rand.nextInt(hi-lo+1)+lo, hi); // Choose pivot randomly and place at end of "a"
double x = a.get(hi);
int i = lo-1;
for (int j=lo; j<hi; j++) {
if (a.get(j) <= x) {
i++;
swap(a, i, j);
}
}
swap(a, i+1, hi);
return i+1;
}
/**
* Swaps two elements in an ArrayList at the specified indices.
*/
private static <E> void swap(ArrayList<E> a, int i, int j) {
E temp = a.get(i);
a.set(i, a.get(j));
a.set(j, temp);
}
/*************************************
********** MAIN METHOD **********
*************************************/
public static void main(String[] args) {
System.err.println("\nClass Methods:\n");
System.err.println("\t" + "select(ArrayList<Integer or Double> a, int orderStatistic)" + "\t" + "Computes the specified order statistic in the list.\n");
System.err.println("\t" + "correlation(ArrayList<Integer> x, ArrayList<Integer> y)" + "\t" + "Computes the correlation coefficient of two lists.\n");
System.err.println("\t" + "mean(ArrayList<Integer> a)" + "\t" + "Computes the mean of a list.\n");
}
}
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