C#返回在字典或列表中指定的序列中满足条件的元素数量 dictionary.count

例如字典重载的方法：Dictionary.Count方法

 
 
Count<KeyValuePair<TKey,
 TValue>>(Func<KeyValuePair<TKey, TValue>, Boolean>)
已重载。 返回一个数字，表示在指定的序列中满足条件的元素数量。 （由 Enumerable 定义。）

		class Pet
            {
                public string Name { get; set; }
                public bool Vaccinated { get; set; }
            }

            public static void CountEx2()
            {
                Pet[] pets = { new Pet { Name="Barley", Vaccinated=true },
                               new Pet { Name="Boots", Vaccinated=false },
                               new Pet { Name="Whiskers", Vaccinated=false } };

                try
                {
                    int numberUnvaccinated = pets.Count(p => p.Vaccinated == false);
                    Console.WriteLine("There are {0} unvaccinated animals.", numberUnvaccinated);
                }
                catch (OverflowException)
                {
                    Console.WriteLine("The count is too large to store as an Int32.");
                    Console.WriteLine("Try using the LongCount() method instead.");
                }
            }