public PlayPrediction Predict(Day data)
{
var playLikelihood = predictLikelihood(avc => avc.Play, data);
var notPlayLikelihood = predictLikelihood(avc => avc.NotPlay, data);
var combinedLiklihood = playLikelihood + notPlayLikelihood;
return playLikelihood > notPlayLikelihood
? new PlayPrediction(true, playLikelihood, playLikelihood / combinedLiklihood)
: new PlayPrediction(false, notPlayLikelihood, notPlayLikelihood / combinedLiklihood);
}
private double predictLikelihood(Func<AttributeValueCount, int> totalGetter, Day data)
{
BigInteger totalInCategory = totalGetter(_totalPerCategory);
var probabilities = _attributes
.Select(a =>
{
var value = a.GetValueFrom(data);
var subTotal = totalGetter(a.ValueCounts[value]);
return Rational.Get(subTotal, totalInCategory);
})
.Concat(new[]
{
Rational.Get(totalInCategory, _total)
}).ToList().AsReadOnly();
return probabilities
.Aggregate((double)1, (a, b) => a*(b.ToDouble()));
}
/* Implementation of Naive Bayes for the Golf/Weather dataset.
* Principles taken from https://www.youtube.com/watch?v=IlVINQDk4o8
* NOTE: The fellow in the video mis-counts "Sunny" (he counts 2 Yes, 3 No instead of 3 Yes, 2 No),
* leading to incorrect probabilities (he calculates 2/9 Yes, 3/5 No rather than 3/9 Yes, 2/5 No) and likelihoods.
*/
public static void Main(string[] args)
{
var dataSet = getTrainingDataSet();
Console.WriteLine("Raw DataSet:");
Writer.DataSetTable(dataSet);
Console.WriteLine();
var summary = new GolfDayPredictor(dataSet);
Console.WriteLine("Naive Bayes has been applied to the DataSet above, which links weather conditions to a decision to play golf or not.");
Console.WriteLine();
Console.WriteLine("Next, we are given a description of weather conditions on an arbitrary day: ");
var novelGolfDay = new Day(Outlook.Sunny, Temp.Cool, Humidity.High, true);
var prediction = summary.Predict(novelGolfDay);
Writer.DataSetRow(novelGolfDay);
Console.WriteLine();
Console.WriteLine("The Naive Bayes learner predicts:");
Console.WriteLine();
Console.Write("\t");
Writer.Prediction(prediction);
Console.WriteLine();
Console.WriteLine("Press any key to exit");
Console.ReadKey();
}
