/**
* @param MultipleTreeNode $node
* @param $branch_name
* @param array $training_data
*/
private function split_node(MultipleTreeNode $node, $branch_name, $training_data)
{
$samples = $training_data['samples'];
$header = $training_data['header'];
$value_count = ArrayService::count_values($samples, $this->base_key);
if (count($value_count) === 1) {
$node->children[$branch_name] = new MultipleTreeNode(strtoupper(key($value_count)));
return;
}
$splitting_attribute = $max_gain = null;
foreach (array_keys($header) as $h) {
$g = $this->get_information_gain($samples, $h);
if ($max_gain === null || $g > $max_gain) {
$max_gain = $g;
$splitting_attribute = $h;
}
}
if ($node->getData() !== null) {
$node->children[$branch_name] = new MultipleTreeNode($splitting_attribute);
$node = $node->children[$branch_name];
} else {
$node->setData($splitting_attribute);
}
$value_count = ArrayService::count_values($samples, $splitting_attribute);
foreach ($value_count as $value_name => $count) {
$subset = ArrayService::create_subset($training_data, $splitting_attribute, $value_name);
$this->split_node($node, $value_name, $subset);
}
return;
}
