List扩展方法汇总（仅备注）

不管在c/s还是b/s的c#语言开发程序中，经常会用到List的扩展方法，尤其在json格式的数据和服务端交互越来越流行，很多时候总是在开发使用到的时候才去搜索有些扩展方法或者linq的用法，在这里，我们只是做一个备注

因为linq没有必要系统的学习，我们只要简单的在list的扩展会使用即可，至少我只这么认为的

本文没有任何技术性，只是备注list或者list泛型的扩展方法，不至于在您不熟悉但是又使用到的时候到处搜索

 public sealed class Employee
    {
        public string Name { get; set; }
        public double Salary { get; set; }
        public short Dependents { get; set; }
    }
    public class Test
    {
        public void FunTest()
        {
            var employees = new List<Employee>
             {
                    new Employee { Name = "Bob", Salary = 1, Dependents = 0 },
                    new Employee { Name = "Sherry", Salary = 2, Dependents = 1 },
                    new Employee { Name = "Kathy", Salary = 3, Dependents = 0 },
                    new Employee { Name = "Joe", Salary = 4, Dependents = 2 },
                    new Employee { Name = "Bob", Salary = 5, Dependents = 0 },
                    new Employee { Name = "Bob", Salary = 6, Dependents = 0 }
             };
            //泛型方法的类型参数是可以省略的

            //所有求和
            double sumSalary = employees.Sum<Employee>(e => e.Salary);//21.0
            //【linq方式】所有求和
            var sumSalary2 = (from v in employees select v).Sum(e => e.Salary);//21.0


            //按照某一条件求和
            double sumSalaryFilter = employees.Where<Employee>(e => e.Name == "Bob").ToList().Sum(e => e.Salary);//12.0
            //【linq方式】按照某一条件求和
            var sumSalaryFilter2 = (from v in employees where v.Name == "Bob" select v).Sum(e => e.Salary);//12.0


            //选择数据而已，即返回自定义改变后的新的投影的数据列表（无法改变源数据）
            var selectChangedNameList = employees.Select<Employee, Employee>(e => { return new Employee { Name = "Bob" }; }).ToList();
            //【linq方式】选择数据而已，即返回自定义改变后的新的投影的数据列表（无法改变源数据）
            var selectChangedNameList2 = (from v in employees select new { Name = "Bob", Salary = v.Salary, Dependents = v.Dependents }).ToList();
            //选择返回某一列的清单投影的数据列表
            var selectSalaryList = employees.Select<Employee, double>(e => { return e.Salary; }).ToList();


            //查找符合条件的第一个元素
            Employee employee1 = employees.Find(e => e.Name == "Bob");
            //【linq方式】查找符合条件的第一个元素
            Employee employee2 = (from v in employees where v.Name == "Bob" select v).First();
            //不用lambda方式筛选符合条件的元素列表
            Predicate<Employee> aaaa = new Predicate<Employee>(fun1);
            List<Employee> employee1List = employees.FindAll(aaaa);
            //lambda方式筛选符合条件的元素列表
            List<Employee> employee2List = employees.FindAll(e => e.Name == "Bob");
            //【linq方式】方式筛选符合条件的元素列表
            List<Employee> employee2List2 = (from v in employees where v.Name == "Bob" select v).ToList();


            //max，min，平均值，筛选满足某条件的max和min已经使用linq方式
            employees.Max(e => e.Salary);
            employees.Min(e => e.Salary);
            (from v in employees select v).Max(e => e.Salary);
            (from v in employees select v).Min(e => e.Salary);
            double maxSalaryFilter = employees.Where<Employee>(e => e.Name == "Bob").ToList().Max(e => e.Salary);

            //简单的运算，比如列表总的相加的值
            var aggregateEmployee = employees.Aggregate<Employee>((result, next) => new Employee { Salary = result.Salary + next.Salary });


            //某一列的不重复的汇总
            var groupEmployees = employees.GroupBy(e => new { e.Name }).Select(g => new { g.Key, Count = g.Count() }).ToList();
            var groupEmployees1 = employees.GroupBy(e => e.Name).Select(e => new { Name = e.Key, sumSalary = e.Sum(d => d.Salary) }).ToList();
            var groupEmployees2 = (from v in employees group v by v.Name into g select new { Name = g.Key, SumSalary = g.Sum(d => d.Salary) }).ToList();


            //查询满足某一条件的所有数据
            IEnumerable<Employee> employee3List = employees.Where<Employee>(e => e.Name == "Bob");
            List<Employee> employee4List = employees.Where<Employee>(e => e.Name == "Bob").ToList();
            employee3List = employee4List as IEnumerable<Employee>;

            Console.WriteLine("adfadsfasdfasdf");
        }


        private bool fun1(Employee e)
        {
            return (e.Name == "Bob");
        }
    }