public function getNodesByLabels(array $labels = array(), $labelizedKeys = false)
    {
        $nodes = [];
        foreach ($labels as $label) {
            $lnodes = $this->getNodesByLabel($label);
            foreach ($lnodes as $node) {
                if ($labelizedKeys) {
                    $nodes[$label] = $node;
                } else {
                    $nodes[] = $node;
                }
            }
        }

        return $nodes;
    }