Rx Sliding Window

gistfile1.cs

static IObservable<string> CheckForFraud(IObservable<string> logins)
{
    return from g in logins.GroupByUntil(l => l, CheckForFraud)
           from c in g.Count()
           where c >= 3
           select g.Key;
}

static IObservable<Unit> CheckForFraud(IGroupedObservable<string, string> g)
{
    var loginAttemptsBeyondTwo = g.Skip(2).Select(_ => Unit.Default);
    var fiveSecondsMax = Observable.Timer(TimeSpan.FromSeconds(5)).Select(_ => Unit.Default);
    return loginAttemptsBeyondTwo.Amb(fiveSecondsMax);
}