// This function is used to find the best split available from this dataset.
// It is meant to be used recusively until we find the ideal tree.
public static (double gain, Question question) FindBestSplit(Dataset dataset)
{
// First, we initialize the values that will be returned
double bestGain = 0;
Question bestQuestion = null;
// We need to save the Gini of the dataset we are working on.
// This is then used to calculate the information gain.
double currentGini = CalculateGini(dataset);
// Remember that Dataset.MaxFeatureCount returns all the features - 1.
// This is because the last column is always used as the label.
int featureCount = dataset.MaxFeatureCount;
// We loop over each feature
for (int i = 0; i < featureCount; ++i)
{
// Get each unique value found in this feature column
HashSet <Feature> features = dataset.GetUniqueValues(i);
// For each of this features, we test creating a Question using
// it. If it is better than the one we already have, we save it
// as the best. At the end, we will have found the best Question
// for this dataset.
foreach (Feature feature in features)
{
Question question = new Question(i, dataset.Headers[i], feature);
(Dataset trueRows, Dataset falseRows) = PartitionDataset(dataset, question);
// If this Question doesn't partition the dataset at all, then we omit the rest
if (trueRows.Count == 0 || falseRows.Count == 0)
{
continue;
}
double gain = CalculateInfoGain(trueRows, falseRows, currentGini);
if (gain > bestGain)
{
bestGain = gain;
bestQuestion = question;
}
}
}
return(bestGain, bestQuestion);
}
private void CreateFieldsFromDataset()
{
// Prevent running if we don't have a tree to analyze
if (tree == null)
{
return;
}
FlowLayoutPanel panel = fieldsPanel;
Dataset dataset = tree.Dataset;
features = new Row(Enumerable.Repeat <Feature>(null, tree.Dataset.MaxFeatureCount).ToList());
// Suspend the layout to prevent re-renders
panel.SuspendLayout();
// Clear the panel before removing any previous text box
panel.Controls.Clear();
// Initialize the List in which we'll save every control to add
List <Control> controls = new List <Control>();
int totalFeatures = dataset.MaxFeatureCount;
// Create a field for each feature
for (int i = 0; i < totalFeatures; ++i)
{
int staticIndex = i;
// Create the Label for this field
Label label = new Label();
label.Text = dataset.Headers[i].FirstCharToUpper();
label.Margin = new Padding(7, 7, 3, 0);
label.AutoSize = true;
controls.Add(label);
// We need different Control types for categorical and numeric features
if (dataset.IsNumeric(i))
{
// Create a NumericUpDown for numeric features
NumericUpDown numericUpDown = new NumericUpDown();
numericUpDown.Minimum = decimal.MinValue;
numericUpDown.Maximum = decimal.MaxValue;
numericUpDown.DecimalPlaces = 2;
numericUpDown.TabStop = true;
numericUpDown.TabIndex = 0;
numericUpDown.Margin = new Padding(10, 3, 3, 3);
// Initialize this feature in 0
features[i] = new Feature(0);
// Set the Event Handler
numericUpDown.ValueChanged += new EventHandler((object sender, EventArgs e) => {
NumericUpDown control = sender as NumericUpDown;
if (features != null)
{
features[staticIndex] = new Feature(control.Value);
}
predictionBtn.Enabled = IsValidPredictionRow(features);
});
panel.SetFlowBreak(numericUpDown, true);
controls.Add(numericUpDown);
}
else
{
// Create the ComboBox for categoric features
ComboBox comboBox = new ComboBox();
comboBox.AutoCompleteMode = AutoCompleteMode.Append;
comboBox.AutoCompleteSource = AutoCompleteSource.ListItems;
comboBox.DropDownStyle = ComboBoxStyle.DropDownList;
comboBox.FormattingEnabled = true;
comboBox.TabStop = true;
comboBox.TabIndex = 0;
comboBox.Margin = new Padding(10, 3, 3, 3);
// Set the Event Handler
comboBox.SelectionChangeCommitted += new EventHandler((object sender, EventArgs e) => {
ComboBox control = sender as ComboBox;
if (features != null && control.SelectedItem != null)
{
features[staticIndex] = new Feature(control.SelectedItem.ToString());
}
predictionBtn.Enabled = IsValidPredictionRow(features);
});
// Get all the unique values for this ComboBox
HashSet <Feature> uniqueFeatures = dataset.GetUniqueValues(i);
string[] values = uniqueFeatures.Select(item => item.ToString()).ToArray();
comboBox.Items.AddRange(values);
panel.SetFlowBreak(comboBox, true);
controls.Add(comboBox);
}
}
// Assign the Enabled property for the Button with the current Row
predictionBtn.Enabled = IsValidPredictionRow(features);
// Display every new control in the UI
panel.Controls.AddRange(controls.ToArray());
// Re-render panels
panel.ResumeLayout(false);
panel.PerformLayout();
}
