Piwik\DataTable\Filter\PivotByDimension::loadSubtable PHP Method

    private function loadSubtable(DataTable $table, Row $row)
    {
        $idSubtable = $row->getIdSubDataTable();
        if ($idSubtable === null) {
            return null;
        }
        $subtable = $row->getSubtable();
        if (!$subtable) {
            $subtable = $this->thisReport->fetchSubtable($idSubtable, $this->getRequestParamOverride($table));
        }
        if (!$subtable) {
            // sanity check
            throw new Exception("Unexpected error: could not load subtable '{$idSubtable}'.");
        }
        return $subtable;
    }