GroupBy<TSource, TKey, TElement> sealed class GroupBy<TSource, TKey, TElement> : Producer<IGroupedObservable<TKey, TElement>, _<TSource, TKey, TElement>> Documentation Code public GroupBy(IObservable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, int? capacity, IEqualityComparer<TKey> comparer)