C:/Documents and Settings/Stephen/Desktop/Biostatistics Library and Program/Biostatistics/KruskalWallisGroupsCollection.cs

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

namespace StephenAshley.Biostatistics
{
   using NUMBER = Decimal;

   public class KruskalWallisGroupsCollection : GroupsCollection
   {
      public KruskalWallisGroupsCollection() : base() { }

      public KruskalWallisGroupsCollection(List<Group> groups) : base(groups) { }

      public override void Add(Group group)
      {
         if (group == null)
            throw new BiostatisticsException(
               "group is a null reference.");

         if (groupsArray != null && k() > 19)
            throw new BiostatisticsException(
               "Addition of Group to a full KruskalWallisGroupsCollection.");

         if (group.n() == 0)
            throw new BiostatisticsException(
               "Group has no members.");

         if (groupsArray == null || k() < 20)
         {
            base.Add(group);
            if (groupsArray != null && k() > 1)
               Initialize();
            return;
         }
      }

      private void Initialize()
      {
         // Make sure we have a valid collection
         if (groupsArray == null)
            throw new BiostatisticsException("groupsArray contains no Groups");
         if (k() < 2)
            throw new BiostatisticsException(
               "Fewer than 2 Groups for Kruskal-Wallis Test.");
         foreach (Group group in groupsArray)
         {
            if (group.n() == 0)
               throw new BiostatisticsException(
                  "KruskalWallisGroupsCollection contains a Group with no members.");
         }

         // Compile a list of all the members of all the Groups
         List<Rank> lstRanks = new List<Rank>();
         for (int i = 0; i < k(); i++)
         {
            foreach (NUMBER decValue in groupsArray[i])
            {
               lstRanks.Add(new Rank(i, decValue, 0));
            }
         }

         // Sort the list
         lstRanks.Sort(Rank.CompareRanks);

         // Assign ranks from 1 to N
         for (int i = 0; i < lstRanks.Count; i++)
         {
            lstRanks[i] = new Rank(lstRanks[i].iGroup, lstRanks[i].decValue,
               (NUMBER)(i + 1));
         }

         // Adjust the ranks for ties
         Int32 iTies = Rank.AdjustTies(ref lstRanks);

         // Compute N()
         iN = 0;
         foreach (Group group in groupsArray)
         {
            iN += group.n();
         }

         // Compute the sum of the ranks for each Group
         R = new NUMBER[k()];
         for (int i = 0; i < k(); i++)
         {
            R[i] = 0.0m;
         }
         foreach (Rank rank in lstRanks)
         {
            R[rank.iGroup] += rank.decRank;
         }

         // Compute H and Hc
         NUMBER decA = 0.0m;
         for (int i = 0; i < k(); i++)
         {
            decA += (NUMBER)(R[i] * R[i]) / (NUMBER)groupsArray[i].n();
         }
         NUMBER decB = 12.0m / (NUMBER)(N() * (N() + 1));
         decH = decB * decA - 3.0m * (N() + 1);

         NUMBER decC = (NUMBER)iTies / (NUMBER)(N() * N() * N() - N());
         decCorrection = 1.0m - decC;

         decHc = decH / decCorrection;


      }

      public Int32 N() { return iN; }

      public NUMBER H() { return decHc; }

      public Int32 DegreesOfFreedom() { return k() - 1; }

      public NUMBER p()
      {
         return (NUMBER)(Distributions.ProbabilityChiSq((double)H(),
             DegreesOfFreedom()));
      }

      private Int32 iN;
      private NUMBER decH;
      private NUMBER decHc;
      private NUMBER decCorrection;

      public NUMBER[] R;
   }
}

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