Chris Donnan

using System;
using System.Collections;
using System.Data;

namespace TradeWeapon.Classification.Bayesian
{
        /// <summary>
        /// Summary description for Class1.
        /// </summary>
        public class NaiveBayesClassifier
        {
                #region fields
                private DataTable sourceData;
                private ArrayList classes = new ArrayList();
                private string classColumnName;
                private const string TABLE_NAME = "source";
                #endregion fields
                #region ctors
                public NaiveBayesClassifier()
                {
                }
                #endregion ctors
                #region public methods
                public void LoadDataSource(DataTable source, string classColName)
                {
                        sourceData = source;
                        classColumnName = classColName;
                        ExtractClasses();
                }
                public void LoadDataSource(DataSet source, string tableName, string classColName)
                {
                        sourceData = source.Tables[ tableName ];
                        LoadDataSource(sourceData,  classColName);
                }
                public void AddToSource(DataRow newRow)
                {
                        AddToSource( newRow, false );
                }
                public void AddToSource(DataRow newRow, bool updateClasses)
                {
                        if(sourceData == null)
                        {
                                throw new NullReferenceException("sourceData has not been initialized");
                        }
                        sourceData.Rows.Add( newRow );
                        if( updateClasses )
                        {
                                ExtractClasses();
                        }
                }
                public DataRow GetPrototypeRow()
                {
                        if(sourceData == null)
                        {
                                throw new NullReferenceException("sourceData has not been initialized");
                        }
                        return sourceData.NewRow();
                }
                /// <summary>
                /// use GetPrototypeRow to get row to populate and add back
                /// </summary>
                /// <param name="unknown"></param>
                /// <returns></returns>
                public string MostLikelyClass(DataRow unknown)
                {
                        string mostLikelyClass = classes[0] as string;
                        double totalCount = Convert.ToDouble( sourceData.Rows.Count );
                        double probability = 0;
                        double bestProbability = 0;
                        foreach(string className in classes)
                        {
                                double countOfClass = Convert.ToDouble( FrequencyOfClass(mostLikelyClass) );
                                probability = countOfClass / totalCount;
                                
                                foreach(DataColumn col in sourceData.Columns)
                                {
                                        string name  = col.ColumnName;
                                        if(name == classColumnName)
                                                continue;
                                        
                                        double count = CountOccurancesWhere(name, unknown[ name ].ToString(), className);
                                        probability *=  (count / countOfClass); 
                                }
                                                                
                                if(probability > bestProbability)
                                {
                                        mostLikelyClass = className;
                                        bestProbability = probability;
                                }
                        }
                        return mostLikelyClass;
                }
                #endregion  public methods
                #region private methods
                private void ExtractClasses()
                {
                        DataTable distinctTable = SelectDistinct(TABLE_NAME, sourceData, classColumnName);
                        foreach (DataRow row in distinctTable.Rows)
                        {
                                classes.Add( row[ classColumnName ] );
                        }
                }
                private int CountOccurances( string attributeName, string attributeValue )
                {
                        string baseString = "[{0}] = '{1}'";
                        string filter =  string.Format(baseString,attributeName,attributeValue);
                        return sourceData.Select(filter).Length;
                }
        
                private int CountOccurancesWhere( string attributeName, string attributeValue, string className )
                {
                        string baseString = "[{0}] = '{1}' and [{2}] == '{3}'";
                        string filter = string.Format(baseString,attributeName,attributeValue , classColumnName, className);
                        return sourceData.Select(filter).Length;
                }       
        
                private int FrequencyOfClass(string className)
                {
                        return CountOccurances( classColumnName, className );
                }
                private DataTable SelectDistinct(string tableName, DataTable sourceTable, string columName)
                {
                        DataTable dt = new DataTable(tableName);
                        dt.Columns.Add(columName, sourceTable.Columns[columName].DataType);
                        object LastValue = null;
                        foreach (DataRow dr in sourceTable.Select("", columName))
                        {
                                if (  LastValue == null || !(ColumnEqual(LastValue, dr[columName])) )
                                {
                                        LastValue = dr[columName];
                                        dt.Rows.Add(new object[]{LastValue});
                                }
                        }
                        return dt;
                }
                private bool ColumnEqual(object A, object B)
                {
                        // Compares two values to see if they are equal. Also compares DBNULL.Value.
                        // Note: If your DataTable contains object fields, then you must extend this
                        // function to handle them in a meaningful way if you intend to group on them.
                        if ( A == DBNull.Value && B == DBNull.Value ) //  both are DBNull.Value
                        {
                                return true;
                        }
                        if ( A == DBNull.Value || B == DBNull.Value ) //  only one is DBNull.Value
                        {
                                return false;
                        }
                        return A.Equals(B);  // value type standard comparison
                }
                #endregion private methods
        }
}