Add statistical mode to auctions

[builder-247]

• Add mode to /skyblock/items/:id endpoint.

Since auctions prices can be thought of as continuous distribution, the prices have to first be split to intervals of equal distance e.g. 5000, 10 000, etc. before calculating mode from these intervals.

core/routes/spec.js

Lines 817 to 851 in 853755b

	route: () => '/skyblock/auctions/:id',
	func: (req, res, cb) => {
	const now = Date.now();
	const from = req.query.from || (now - 24 * 60 * 60 * 1000);
	const until = req.query.until || now;
	if (Number.isNaN(Number(from))) {
	return cb(res.status(400).json({ error: "parameter 'from' must be an integer" }));
	}
	redis.zrangebyscore(req.params.id, from, until, (err, auctions) => {
	if (err) {
	logger.error(err);
	}
	const obj = {
	average_price: 0,
	median_price: 0,
	standard_deviation: 0,
	min_price: 0,
	max_price: 0,
	sold: 0,
	auctions: {},
	};
	const priceArray = [];
	auctions.forEach((auction) => {
	auction = JSON.parse(auction);
	if (auction.bids.length > 0) priceArray.push(auction.highest_bid_amount / auction.item.count);
	obj.auctions[auction.end] = auction;
	});
	obj.average_price = average(priceArray);
	obj.median_price = median(priceArray);
	obj.standard_deviation = stdDev(priceArray);
	obj.min_price = min(priceArray);
	obj.max_price = max(priceArray);
	obj.sold = priceArray.length;
	return res.json(obj);
	});