C# List GroupBy 分组统计

1、 按某一字段进行分组并返回每一组的记录数目

List list = new List()  
            {  
                new DbInfo(){ DbId=1,HostId=1 },      
                new DbInfo(){ DbId=2,HostId=1 },  
                new DbInfo(){ DbId=3,HostId=2 },  
                new DbInfo(){ DbId=4,HostId=2 }  
            };

            var result = list.GroupBy(d => d.HostId);
            var ee = result.Where(d => d.Key == 1).FirstOrDefault() == null ? 0 : result.Where(d => d.Key == 1).FirstOrDefault().Count();
            Console.WriteLine(ee);
            Console.ReadLine();