public static 数据结构.IEnumerable <系统内置接口.IGrouping <TKey, TSource> > GroupBy <TSource, TKey>(this IEnumerable <TSource> source, 内置委托.Func <TSource, TKey> keyselector) { MyLookup <TKey, TSource> lookup = new MyLookup <TKey, TSource>(null); lookup.Create(source, keyselector, IdentityFunction <TSource> .Instance); return(lookup.GetPerGroup()); }