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HSQLDB example source code file (ArrayCounter.java)

This example HSQLDB source code file (ArrayCounter.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - HSQLDB tags/keywords

arraycounter, arraycounter

The HSQLDB ArrayCounter.java source code

/* Copyright (c) 2001-2008, The HSQL Development Group
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * Neither the name of the HSQL Development Group nor the names of its
 * contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL HSQL DEVELOPMENT GROUP, HSQLDB.ORG,
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */


package org.hsqldb.lib;

/**
 * Collection of routines for counting the distribution of the values
 * in an int[] array.
 *
 * @author fredt@users
 * @version 1.7.2
 * @since 1.7.2
 */
public class ArrayCounter {

    /**
     * Returns an int[] array of length segments containing the distribution
     * count of the elements in unsorted int[] array with values between min
     * and max (range). Values outside the min-max range are ignored<p>
     *
     * A usage example is determining the count of people of each age group
     * in a large int[] array containing the age of each person. Called with
     * (array, 16,0,79), it will return an int[16] with the first element
     * the count of people aged 0-4, the second element the count of those
     * aged 5-9, and so on. People above the age of 79 are excluded. If the
     * range is not a multiple of segments, the last segment will be cover a
     * smaller sub-range than the rest.
     *
     */
    public static int[] countSegments(int[] array, int elements,
                                      int segments, int start, int limit) {

        int[] counts   = new int[segments];
        long  interval = calcInterval(segments, start, limit);
        int   index    = 0;
        int   element  = 0;

        if (interval <= 0) {
            return counts;
        }

        for (int i = 0; i < elements; i++) {
            element = array[i];

            if (element < start || element >= limit) {
                continue;
            }

            index = (int) ((element - start) / interval);

            counts[index]++;
        }

        return counts;
    }

    /**
     * With an unsorted int[] array and with target a positive integer in the
     * range (1,array.length), finds the value in the range (start,limit) of the
     * largest element (rank) where the count of all smaller elements in that
     * range is less than or equals target. Parameter margin indicates the
     * margin of error in target<p>
     *
     * In statistics, this can be used to calculate a median or quadrile value.
     * A usage example applied to an array of age values is to determine
     * the maximum age of a given number of people. With the example array
     * given in countSegments, rank(array, c, 6000, 18, 65, 0) will return an age
     * value between 18-64 (inclusive) and the count of all people aged between
     * 18 and the returned value(exclusive) will be less than or equal 6000.
     *
     */
    public static int rank(int[] array, int elements, int target, int start,
                           int limit, int margin) {

        final int segments     = 256;
        int       elementCount = 0;
        int       currentLimit = limit;

        for (;;) {
            long interval = calcInterval(segments, start, currentLimit);
            int[] counts = countSegments(array, elements, segments, start,
                                         currentLimit);

            for (int i = 0; i < counts.length; i++) {
                if (elementCount + counts[i] < target) {
                    elementCount += counts[i];
                    start        += interval;
                } else {
                    break;
                }
            }

            if (elementCount + margin >= target) {
                return start;
            }

            if (interval <= 1) {
                return start;
            }

            currentLimit = start + interval < limit ? (int) (start + interval)
                                                    : limit;
        }
    }

    /**
     * Helper method to calculate the span of the sub-interval. Simply returns
     * the cieling of ((limit - start) / segments) and accounts for invalid
     * start and limit combinations.
     */
    static long calcInterval(int segments, int start, int limit) {

        long range = limit - start;

        if (range < 0) {
            return 0;
        }

        int partSegment = (range % segments) == 0 ? 0
                                                  : 1;

        return (range / segments) + partSegment;
    }
}

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