IEnumerable<T> datas; // 何かデータ取得処理 ・・・ var sw = new Stopwatch(); sw.Start(); var array = datas.ToArray(); sw.Stop(); Console.WriteLine("Array変換:{0}", sw.Elapsed); sw.Reset(); sw.Start(); var list = datas.ToList(); sw.Stop(); Console.WriteLine("List変換:{0}", sw.Elapsed); sw.Reset(); sw.Start(); var dictionary = datas.ToDictionary(x => x.Id); sw.Stop(); Console.WriteLine("Dictionary変換:{0}", sw.Elapse