Counting the distribution of the values in an array. : Array Util « Collections Data Structure « C# / C Sharp

1. C# / C Sharp
2. Collections Data Structure
3. Array Util

Counting the distribution of the values in an array.

  
   
//
// (C) Copyright 2009 Irantha Suwandarathna (irantha@gmail.com)
// All rights reserved.
//

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace EffiProz.Core.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)
        {

            const 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 += (int)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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