Our exchanges have multiple markets inside, and that's the abstraction we will define now. A Market has various private attributes, as we saw before when we defined what data is expected from each file, and that's the same data we see in our constructor. It also offers a data() method to send back a list with the data that should be saved to a database. Finally, it provides setters and getters as required. Note that the setter for the price depends on what units are requested, which can be either usd or btc, to get a market's asset price in terms of US Dollars or Bitcoin, respectively:
Market <- R6Class( "Market", public = list( initialize = function(timestamp, name, symbol, rank, price_btc, price_usd) ...
