Computes the correlation between two arrays of the same length, p and q. - Java java.lang

Java examples for java.lang:Math Array Function

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Description

Computes the correlation between two arrays of the same length, p and q.

Demo Code

/** A collection of mathematical utility functions.
 * <p>/*w  ww .  j  a  v a2  s  .co m*/
 * Copyright (c) 2008 Eric Eaton
 * <p>
 * This program 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
 * (at your option) any later version.
 * <p>
 * This program 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.
 * <p>
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see http://www.gnu.org/licenses/.
 * 
 * @author Eric Eaton (EricEaton@umbc.edu) <br>
 *         University of Maryland Baltimore County
 * 
 * @version 0.1
 *
 */
//package com.java2s;

public class Main {
    /** Computes the correlation between two arrays of the same length, p and q.
     * Computes the correlation between p and q as
     * r = (|p| * \sum_i(p[i]*q[i]) - \sum_i(p[i]) * \sum_i(q[i]))/
     *      sqrt((|p| * \sum_i((p[i])^2) - (\sum_i(p[i]))^2) *
     *           (|p| * \sum_i((p[i])^2) - (\sum_i(p[i]))^2))
     * This correlation can be tested for statistical significance via t-tests. 
     * See e.g.: http://www.socialresearchmethods.net/kb/statcorr.htm
     * @return The correlation between the elements of the two arrays.
     */
    public static double correlation(int[] p, int[] q) {

        if (p == null || q == null) {
            throw new IllegalArgumentException("p and q cannot be null");
        }
        if (p.length != q.length) {
            throw new IllegalArgumentException(
                    "p and q must be the same length");
        }

        // compute the sums and squared sums
        int sumP = 0;
        int sumQ = 0;
        int sumPSquared = 0;
        int sumQSquared = 0;
        int sumPQ = 0;
        for (int i = 0; i < p.length; i++) {
            sumP += p[i];
            sumQ += q[i];
            sumPSquared += p[i] * p[i];
            sumQSquared += q[i] * q[i];
            sumPQ += p[i] * q[i];
        }

        // compute the correlation
        double r = ((double) (p.length * sumPQ - sumP * sumQ))
                / Math.sqrt(((long) (p.length * sumPSquared - sumP * sumP))
                        * ((long) (p.length * sumQSquared - sumQ * sumQ)));

        return r;
    }

    /** Computes the correlation between two arrays of the same length, p and q.
     * Computes the correlation between p and q as
     * r = (|p| * \sum_i(p[i]*q[i]) - \sum_i(p[i]) * \sum_i(q[i]))/
     *      sqrt((|p| * \sum_i((p[i])^2) - (\sum_i(p[i]))^2) *
     *           (|p| * \sum_i((p[i])^2) - (\sum_i(p[i]))^2))
     * This correlation can be tested for statistical significance via t-tests. 
     * See e.g.: http://www.socialresearchmethods.net/kb/statcorr.htm
     * @return The correlation between the elements of the two arrays.
     */
    public static double correlation(double[] p, double[] q) {

        if (p == null || q == null) {
            throw new IllegalArgumentException("p and q cannot be null");
        }
        if (p.length != q.length) {
            throw new IllegalArgumentException(
                    "p and q must be the same length");
        }

        // compute the sums and squared sums
        double sumP = 0;
        double sumQ = 0;
        double sumPSquared = 0;
        double sumQSquared = 0;
        double sumPQ = 0;
        for (int i = 0; i < p.length; i++) {
            sumP += p[i];
            sumQ += q[i];
            sumPSquared += p[i] * p[i];
            sumQSquared += q[i] * q[i];
            sumPQ += p[i] * q[i];
        }

        // compute the correlation
        double r = (p.length * sumPQ - sumP * sumQ)
                / Math.sqrt((p.length * sumPSquared - sumP * sumP)
                        * (p.length * sumQSquared - sumQ * sumQ));

        return r;
    }
}

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