public function sortDepth(string $symbol, int $limit = 11)
    {
        $bids = $this->depthCache[$symbol]['bids'];
        $asks = $this->depthCache[$symbol]['asks'];
        krsort($bids);
        ksort($asks);
        return [
            "asks" => array_slice($asks, 0, $limit, true),
            "bids" => array_slice($bids, 0, $limit, true),
        ];
    }