/**
* Given the data of the historic users and the current ones, creates a matrix of association coefficients, with the
* current users as rows, and the historic user as columns.
*
* @see cosine_similarity($vector1, $vector2).
* @param array $currentdata A 2D array.
* @param array $historicdata A 2D array.
* @param \text_progress_trace $trace Text output trace.
* @return array The association matrix; empty if no association could be made.
*/
public function create_associations_matrix($currentdata, $historicdata, $trace)
{
$db = new database_helper();
$trace->output("[mycourse " . date('d/m/Y H:i:s') . "]: Starting creation of associations matrix.");
$trace->output("[mycourse " . date('d/m/Y H:i:s') . "]: Transforming receiving data to get a matrix of users x resources. " . " with the views as values.");
$currenttransformeddata = $this->matrix->transform_queried_data($currentdata);
$historictransformeddata = $this->matrix->transform_queried_data($historicdata);
$trace->output('[mycourse ' . date('d/m/Y H:i:s') . ']: Both historic and current data have been transformed.');
$currentusers = array_keys($currenttransformeddata);
$historicusers = array_keys($historictransformeddata);
$matrix = array();
foreach ($currentusers as $currentuser) {
$trace->output('[mycourse ' . date('d/m/Y H:i:s') . "]: Starting calculating associations for current user " . "{$currentuser}.");
$currentviewsvector = $currenttransformeddata[$currentuser];
$similarities = null;
foreach ($historicusers as $historicuser) {
$historicviewsvector = $historictransformeddata[$historicuser];
$trace->output('[mycourse ' . date('d/m/Y H:i:s') . "]: Starting calculating cosine similarity between a vector " . "of " . count($currentviewsvector) . " elements with a vector of " . count($historicviewsvector) . " elements.");
$similarity = $this->cosine_similarity($currentviewsvector, $historicviewsvector);
$trace->output('[mycourse ' . date('d/m/Y H:i:s') . ']: Cosine similarity between those vectors has been ' . 'calculated.');
$similarity = round($similarity, 4);
$similarities[$historicuser] = $similarity;
$db->insert_similarity($currentuser, $historicuser, $similarity, $this->currentweek);
}
$matrix[$currentuser] = $similarities;
$trace->output('[mycourse ' . date('d/m/Y H:i:s') . "]: Similarities for current user {$currentuser} have been " . "calculated.");
}
return $matrix;
}
