//Gathers the required counts for the features and performs feature selection
private FeaturesStatistics selectFeatures(List <Document> dataset, int numberOfFeatures = 30)
{
FeatureExtraction featureExtractor = new FeatureExtraction();
//the FeatureStatistica object contains statistics about all the features found in the documents
FeaturesStatistics statistics = featureExtractor.extractFeatureStatistics(dataset);
//we pass this information to the feature selection algorithm and we get a list with the selected features
Dictionary <String, Double> selectedFeatures = featureExtractor.select(statistics, numberOfFeatures);
Dictionary <String, Dictionary <String, int> > newfeatureCategoryJointCount = new Dictionary <string, Dictionary <string, int> >();
//clip from the stats all the features that are not selected
foreach (var arr in statistics.featureCategoryJointCount)
{
if (selectedFeatures.ContainsKey(arr.Key))
{
newfeatureCategoryJointCount.Add(arr.Key, arr.Value);
}
}
statistics.featureCategoryJointCount = newfeatureCategoryJointCount;
return(statistics);
}
public FeaturesStatistics extractFeatureStatistics(List <Document> dataset)
{
FeaturesStatistics statistics = new FeaturesStatistics();
int categoryCount;
List <String> categories;
int featureCategoryCount;
Dictionary <String, int> featureCategoryCounts;
foreach (Document doc in dataset)
{
statistics.countOfDocuments++; //increase the number of documents
categories = doc.categories;
foreach (var category in categories)
{
//increase the category counter by one
if (statistics.categoryCounts.ContainsKey(category))
{
categoryCount = statistics.categoryCounts[category];
statistics.categoryCounts[category] = ++categoryCount;
}
else
{
statistics.categoryCounts.Add(category, 1);
}
foreach (var feature in doc.tokens)
{
//get the counts of the feature in the categories
if (statistics.featureCategoryJointCount.ContainsKey(feature.Key))
{
featureCategoryCounts = statistics.featureCategoryJointCount[feature.Key];
}
else
{
//initialize it if it does not exist
statistics.featureCategoryJointCount.Add(feature.Key, new Dictionary <String, int>());
}
if (statistics.featureCategoryJointCount[feature.Key].ContainsKey(category))
{
featureCategoryCount = statistics.featureCategoryJointCount[feature.Key][category];
statistics.featureCategoryJointCount[feature.Key][category] = ++featureCategoryCount;
}
else
{
featureCategoryCount = 0;
statistics.featureCategoryJointCount[feature.Key].Add(category, ++featureCategoryCount);
}
}
}
}
return(statistics);
}
public void train(Dictionary <String, Double> categoryPriors, int numberOfFeatures = 1000)
{
Console.WriteLine("Training......");
//preprocess the given dataset
List <Document> dataset = preprocessDataset(Program.datasetsDirectory);
//produce the feature stats and select the best features
FeaturesStatistics featureStatistics = selectFeatures(dataset);
//intiliaze the knowledgeBase of the classifier
knowledgeBase = new KnowledgeBase();
knowledgeBase.countOfDocuments = featureStatistics.countOfDocuments; //number of observations
knowledgeBase.numberOfFeatures = featureStatistics.featureCategoryJointCount.Count; //number of features
//check is prior probabilities are given
if (categoryPriors == null)
{
//if not estimate the priors from the sample
knowledgeBase.numberOfCategories = featureStatistics.categoryCounts.Count; //number of cateogries
knowledgeBase.logPriors = new Dictionary <string, double>();
foreach (var item in featureStatistics.categoryCounts)
{
//knowledgeBase.logPriors.Add(item.Key, Math.Log10((double)item.Value / knowledgeBase.countOfDocuments));
knowledgeBase.logPriors.Add(item.Key, (double)item.Value / knowledgeBase.countOfDocuments);
}
}
else
{
knowledgeBase.numberOfCategories = categoryPriors.Count;
//make sure that the given priors are valid
if (knowledgeBase.numberOfCategories != featureStatistics.categoryCounts.Count)
{
throw new ArgumentException("Invalid priors Array: Make sure you pass a prior probability for every supported category.");
}
foreach (var item in categoryPriors)
{
if (item.Value < 0)
{
throw new ArgumentException("Invalid priors Array: Prior probabilities should be between 0 and 1.");
}
//knowledgeBase.logPriors.Add(item.Key, Math.Log10(item.Value));
knowledgeBase.logPriors.Add(item.Key, item.Value);
}
}
//We are performing laplace smoothing (also known as add-1). This requires to estimate the total feature occurrences in each category
Dictionary <String, int> featureOccurrencesInCategory = new Dictionary <string, int>();
int featureOccSum, allWordsCount = 0;
foreach (var category in knowledgeBase.logPriors)
{
featureOccSum = 0;
foreach (var categoryListOccurrences in featureStatistics.featureCategoryJointCount.Values)
{
if (categoryListOccurrences.ContainsKey(category.Key))
{
int occurrences = categoryListOccurrences[category.Key];
featureOccSum += occurrences;
allWordsCount += occurrences;
}
}
if (featureOccurrencesInCategory.ContainsKey(category.Key))
{
featureOccurrencesInCategory[category.Key] = featureOccSum;
}
else
{
featureOccurrencesInCategory.Add(category.Key, featureOccSum);
}
}
//estimate log likelihoods
int count, negativeCount, allWordsInCategory;
Dictionary <String, int> featureCategoryCounts = new Dictionary <string, int>();
double logLikelihood;
foreach (String category in knowledgeBase.logPriors.Keys)
{ ///<feature, <category, count>>
foreach (var entry in featureStatistics.featureCategoryJointCount)
{
featureCategoryCounts = entry.Value;
negativeCount = 0;
foreach (string cat in featureCategoryCounts.Keys)
{
if (cat != category)
{
negativeCount += featureCategoryCounts[cat];
}
}
if (featureCategoryCounts.ContainsKey(category))
{
count = featureCategoryCounts[category];
}
else
{
count = 0;
}
if (featureOccurrencesInCategory.ContainsKey(category))
{
allWordsInCategory = featureOccurrencesInCategory[category];
}
else
{
allWordsInCategory = 0;
}
double PInClassC = (count + 1.0) / (allWordsInCategory + knowledgeBase.numberOfFeatures);
double PisNotInClassC = (negativeCount + 1.0) / ((allWordsCount - allWordsInCategory) + knowledgeBase.numberOfFeatures);
logLikelihood = Math.Log10(PInClassC / (PisNotInClassC)); //log(x/y) = logX - logY
if (knowledgeBase.logConditionalProbability.ContainsKey(entry.Key))
{
knowledgeBase.logConditionalProbability[entry.Key].Add(category, logLikelihood);
}
else
{
knowledgeBase.logConditionalProbability.Add(entry.Key, new Dictionary <String, Double>());
knowledgeBase.logConditionalProbability[entry.Key].Add(category, logLikelihood);
}
}
}
featureOccurrencesInCategory = null;
string baseDirPath = Path.GetDirectoryName(Path.GetDirectoryName(System.IO.Directory.GetCurrentDirectory()));
string fileName = baseDirPath + "\\" + ConfigurationManager.AppSettings["knowledgeBase"];
var knowledgeBaseStr = JsonConvert.SerializeObject(this.knowledgeBase);
File.WriteAllText(fileName, knowledgeBaseStr, Encoding.UTF8);
Console.WriteLine("\n\nDone Training !");
Console.Beep();
}
public Dictionary <String, Double> select(FeaturesStatistics statistics, int numberOfFeatures = 50)
{
Dictionary <String, Double> selectedFeatures = new Dictionary <string, double>();
String feature;
String category;
Dictionary <String, int> categoryList;
double Ndot0, Ndot1, N1dot, N0dot, N00, N01, N10, N11;
double N = statistics.countOfDocuments + 0.0;
double chisquareScore;
double score;
//Double previousScore;
Dictionary <string, Dictionary <string, double> > selectedFeaturesForCategory = new Dictionary <string, Dictionary <string, double> >();
foreach (var featureCategoryCounts in statistics.featureCategoryJointCount)
{
feature = featureCategoryCounts.Key;
categoryList = featureCategoryCounts.Value;
//calculate the N1. (number of documents that have the feature)
N1dot = 0;
foreach (int count in categoryList.Values)
{
N1dot += count;
}
//also the N0. (number of documents that DONT have the feature)
N0dot = statistics.countOfDocuments - N1dot;
if (feature == "coffe")
{
Console.WriteLine(String.Format("N0.={0}, N0.={1}\n N={2}", N0dot, N1dot, N));
}
foreach (var categoryCounts in categoryList)
{
category = categoryCounts.Key;
N11 = categoryCounts.Value; //N11 is the number of documents that have the feature and belong on the specific category
N01 = statistics.categoryCounts[category] - N11; //N01 is the total number of documents that do not have the particular feature BUT they belong to the specific category
N00 = N0dot - N01; //N00 counts the number of documents that don't have the feature and don't belong to the specific category
N10 = N1dot - N11; //N10 counts the number of documents that have the feature and don't belong to the specific category
N10 = N10 == 0.0 ? 1.0 : N10;
N01 = N01 == 0.0 ? 1.0 : N01;
Ndot0 = N10 + N00;
Ndot1 = N11 + N01;
//calculate the chisquare score based on the above statistics
chisquareScore = N * Math.Pow(N11 * N00 - N10 * N01, 2) / ((N11 + N01) * (N11 + N10) * (N10 + N00) * (N01 + N00));
score = (N11 / N) * Math.Log((N * N11) / (N1dot * Ndot1), 2);
score += (N01 / N) * Math.Log((N * N01) / (N0dot * Ndot1), 2);
score += (N10 / N) * Math.Log((N * N10) / (N1dot * Ndot0), 2);
score += (N00 / N) * Math.Log((N * N00) / (N0dot * Ndot0), 2);
if (category == "coffee")
{
Console.WriteLine(String.Format("N01={0}, N11={1}\n N00={2}, N10={3} \n Ndot0={4}, Ndot1={5} \n N0dot={6}, N1dot={7} \n score={8}", N01, N11, N00, N10, Ndot0, Ndot1, N0dot, N1dot, score));
}
if (selectedFeaturesForCategory.ContainsKey(category))
{
if (!selectedFeaturesForCategory[category].ContainsKey(feature))
{
selectedFeaturesForCategory[category].Add(feature, score);
}
}
else
{
selectedFeaturesForCategory.Add(category, new Dictionary <string, double>());
selectedFeaturesForCategory[category].Add(feature, score);
}
////if the score is larger than the critical value then add it in the list
//if (chisquareScore >= numberOfFeatures)
//{
// previousScore = selectedFeatures[feature];
// if (previousScore == null || chisquareScore > previousScore)
// {
// selectedFeatures.Add(feature, chisquareScore);
// }
//}
}
}
foreach (var cat in selectedFeaturesForCategory.Keys)
{
Dictionary <string, double> features = selectedFeaturesForCategory[cat];
List <KeyValuePair <String, double> > list = features.ToList();
list.Sort((pair1, pair2) => { return(pair2.Value.CompareTo(pair1.Value)); });
foreach (var l in list.Take(numberOfFeatures))
{
//if (cat == "coffee") {
// foreach (var f in selectedFeaturesForCategory[cat])
// Console.WriteLine(String.Format("{0},{1}",f.Key,f.Value));
// }
if (!selectedFeatures.ContainsKey(l.Key))
{
selectedFeatures.Add(l.Key, l.Value);
}
}
}
return(selectedFeatures);
}
