<PackageReference Include="System.Reactive" Version="5.0.0-preview.220" />

IGroupedObservable<TKey, TElement>

public interface IGroupedObservable<TKey, TElement> : IObservable<TElement>
Represents an observable sequence of elements that have a common key.
using System.Runtime.CompilerServices; namespace System.Reactive.Linq { [System.Runtime.CompilerServices.NullableContext(1)] public interface IGroupedObservable<[System.Runtime.CompilerServices.Nullable(2)] out TKey, [System.Runtime.CompilerServices.Nullable(2)] out TElement> : IObservable<TElement> { TKey Key { get; } } }