Mega Code Archive
Counting the distribution of the values in an array
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//
// (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;
}
}
}
]]>