<PackageReference Include="System.Reactive" Version="7.0.0-preview.16" />

System.Reactive.Linq.IGroupedObservable<TKey, TElement>

public interface IGroupedObservable<TKey, TElement> : IObservable<TElement>
namespace System.Reactive.Linq { public interface IGroupedObservable<[System.Runtime.CompilerServices.Nullable(2)] out TKey, [System.Runtime.CompilerServices.Nullable(2)] out TElement> : IObservable<TElement> { TKey Key { get; } } }