system.reactive Getting started with system.reactive Sharing a single subscription (Publish)

Example

Given an IObservable<Offer> of offers from merchants to buy or sell some type of item at a fixed price, we can match pairs of buyers and sellers as follows:

var sellers = offers.Where(offer => offer.IsSell).Select(offer => offer.Merchant);
var buyers = offers.Where(offer => offer.IsBuy).Select(offer => offer.Merchant);
var trades = Observable.Zip(sellers, buyers, (seller, buyer) => new Trade(seller, buyer));

The problem with this is that each subscription to trades will subscribe to offers twice. We can make sellers and buyers share a single subscription to offers by using Publish:

var trades = offers.Publish(_offers =>
{
    var sellers = _offers.Where(offer => offer.IsSell).Select(offer => offer.User);
    var buyers = _offers.Where(offer => offer.IsBuy).Select(offer => offer.User);
    return Observable.Zip(sellers, buyers, (seller, buyer) => new Trade(seller, buyer));
});