internal class GroupByOperator<TSource, TKey> : IObservable<IGroupedObservable<TKey, TSource>>
{
    private IObservable<TSource> source;
    private Func<TSource, TKey> keySelector;
    public GroupByOperator(IObservable<TSource> source, Func<TSource, TKey> keySelector)
    {
        this.source = source;
        this.keySelector = keySelector;
    }

    public IDisposable Subscribe(IObserver<IGroupedObservable<TKey, TSource>> observer)
    {
        var grouper = new Grouper(observer, this.keySelector);
        return source.Subscribe(grouper);
    }