System.Linq.Lookup<TKey, TElement>

Lookup<TKey, TElement>

public class Lookup<TKey, TElement> : IEnumerable<IGrouping<TKey, TElement>>, IEnumerable, ILookup<TKey, TElement>

public int Count { get; }

public IEnumerable<TElement> this[TKey key] { get; }

public IEnumerable<TResult> ApplyResultSelector<TResult>(Func<TKey, IEnumerable<TElement>, TResult> resultSelector)

public bool Contains(TKey key)