public GroupCollectionViewModel(IObservable <IGroupChangeSet <TGroupable, TKey, TGroupKey> > changeSet)
    {
        collection = GroupHelper
                     .ConvertGroups <TGroupable, T, TKey, TGroupKey>(changeSet)
                     .OnSelectableItemAdded()
                     .ToCollection(out var disposable);

        CompositeDisposable.Add(disposable);
    }
 public GroupCollection2ViewModel(IObservable <IChangeSet <IGroup <TGroupable, TGroupKey> > > changeSet)
 {
     Collection = GroupHelper.ConvertGroups <TGroupable, T, TGroupKey>(changeSet).ToCollection(CompositeDisposable);
 }