Source Code Cross Referenced for ArrayCounter.java in  » Database-DBMS » hsql » org » hsqldb » lib » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Database DBMS » hsql » org.hsqldb.lib 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /* Copyright (c) 2001-2005, The HSQL Development Group
002:         * All rights reserved.
003:         *
004:         * Redistribution and use in source and binary forms, with or without
005:         * modification, are permitted provided that the following conditions are met:
006:         *
007:         * Redistributions of source code must retain the above copyright notice, this
008:         * list of conditions and the following disclaimer.
009:         *
010:         * Redistributions in binary form must reproduce the above copyright notice,
011:         * this list of conditions and the following disclaimer in the documentation
012:         * and/or other materials provided with the distribution.
013:         *
014:         * Neither the name of the HSQL Development Group nor the names of its
015:         * contributors may be used to endorse or promote products derived from this
016:         * software without specific prior written permission.
017:         *
018:         * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
019:         * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
020:         * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
021:         * ARE DISCLAIMED. IN NO EVENT SHALL HSQL DEVELOPMENT GROUP, HSQLDB.ORG,
022:         * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
023:         * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
024:         * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025:         * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
026:         * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027:         * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028:         * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029:         */
030:
031:        package org.hsqldb.lib;
032:
033:        /**
034:         * Collection of routines for counting the distribution of the values
035:         * in an int[] array.
036:         *
037:         * @author fredt@users
038:         * @version 1.7.2
039:         * @since 1.7.2
040:         */
041:        public class ArrayCounter {
042:
043:            /**
044:             * Returns an int[] array of length segments containing the distribution
045:             * count of the elements in unsorted int[] array with values between min
046:             * and max (range). Values outside the min-max reange are ignored<p>
047:             *
048:             * A usage example is determining the count of people of each age group
049:             * in a large int[] array containing the age of each person. Called with
050:             * (array, 16,0,79), it will return an int[16] with the first element
051:             * the count of people aged 0-4, the second element the count of those
052:             * aged 5-9, and so on. People above the age of 79 are excluded. If the
053:             * range is not a multiple of segments, the last segment will be cover a
054:             * smaller sub-range than the rest.
055:             *
056:             */
057:            public static int[] countSegments(int[] array, int elements,
058:                    int segments, int start, int limit) {
059:
060:                int[] counts = new int[segments];
061:                long interval = calcInterval(segments, start, limit);
062:                int index = 0;
063:                int element = 0;
064:
065:                if (interval <= 0) {
066:                    return counts;
067:                }
068:
069:                for (int i = 0; i < elements; i++) {
070:                    element = array[i];
071:
072:                    if (element < start || element >= limit) {
073:                        continue;
074:                    }
075:
076:                    index = (int) ((element - start) / interval);
077:
078:                    counts[index]++;
079:                }
080:
081:                return counts;
082:            }
083:
084:            /**
085:             * With an unsorted int[] array and with target a positive integer in the
086:             * range (1,array.length), finds the value in the range (start,limit) of the
087:             * largest element (rank) where the count of all smaller elements in that
088:             * range is less than or equals target. Parameter margin indicates the
089:             * margin of error in target<p>
090:             *
091:             * In statistics, this can be used to calculate a median or quadrile value.
092:             * A usage example applied to an array of age values is to determine
093:             * the maximum age of a given number of people. With the example array
094:             * given in countSegments, rank(array, c, 6000, 18, 65, 0) will return an age
095:             * value between 18-64 (inclusive) and the count of all people aged between
096:             * 18 and the returned value(exclusive) will be less than or equal
097:             * 6000.
098:             *
099:             */
100:            public static int rank(int[] array, int elements, int target,
101:                    int start, int limit, int margin) {
102:
103:                final int segments = 256;
104:                int elementCount = 0;
105:                int currentLimit = limit;
106:
107:                for (;;) {
108:                    long interval = calcInterval(segments, start, currentLimit);
109:                    int[] counts = countSegments(array, elements, segments,
110:                            start, currentLimit);
111:
112:                    for (int i = 0; i < counts.length; i++) {
113:                        if (elementCount + counts[i] < target) {
114:                            elementCount += counts[i];
115:                            start += interval;
116:                        } else {
117:                            break;
118:                        }
119:                    }
120:
121:                    if (elementCount + margin >= target) {
122:                        return start;
123:                    }
124:
125:                    if (interval <= 1) {
126:                        return start;
127:                    }
128:
129:                    currentLimit = start + interval < limit ? (int) (start + interval)
130:                            : limit;
131:                }
132:            }
133:
134:            /**
135:             * Helper method to calculate the span of the sub-interval. Simply returns
136:             * the cieling of ((limit - start) / segments) and accounts for invalid
137:             * start and limit combinations.
138:             */
139:            static long calcInterval(int segments, int start, int limit) {
140:
141:                long range = limit - start;
142:
143:                if (range < 0) {
144:                    return 0;
145:                }
146:
147:                int partSegment = (range % segments) == 0 ? 0 : 1;
148:
149:                return (range / segments) + partSegment;
150:            }
151:        }
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