public class MainViewModel : ViewModelBase
{
    private readonly SourceList<TeamMember> _sourceList = new SourceList<TeamMember>();
    [Reactive] public int OnlineCount { get; set; }
    [Reactive] public ReadOnlyObservableCollection<TeamMember> TeamMembers { get; private set; }
    public MainViewModel()
    {
        var pub = _sourceList.Connect().ObserveOn(RxApp.MainThreadScheduler).Publish().RefCount();
        pub.Bind(out var teamMembers).Subscribe();
        TeamMembers = teamMembers;

        pub.AutoRefreshOnObservable(x => x.WhenAnyValue(y => y.Online))
            .Filter(x => x.Online)
            .Count()
            .Subscribe(x => OnlineCount = x);

        Observable.Interval(TimeSpan.FromSeconds(1)).Do(_ =>
           {
               _sourceList.Edit(list =>
               {
                   foreach (var member in list)
                   {
                       member.Online = new Random().Next(0, 2) == 1;
                   }
               });
           }).Subscribe();

        MakeData();
    }

    private void MakeData()
    {
        AddMember("Alice", "Developer");
        AddMember("Bob", "Designer");
        AddMember("Charlie", "Manager");
        AddMember("Diana", "Tester");
        AddMember("Ethan", "DevOps");
        AddMember("Fiona", "Product Owner");
    }

    private void AddMember(string name, string role) => _sourceList.Add(new TeamMember { Name = name, Role = role, Online = false });
}
public class TeamMember : ReactiveObject
{
    [Reactive] public string Name { get; set; } = string.Empty;
    [Reactive] public string Role { get; set; } = string.Empty;
    [Reactive] public bool Online { get; set; }
}