ToLookup<TSource, TKey, TElement> sealed class ToLookup<TSource, TKey, TElement> : Producer<ILookup<TKey, TElement>, _<TSource, TKey, TElement>> Documentation Code public ToLookup(IObservable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, IEqualityComparer<TKey> comparer)