C#中的lamda實用的select用法

1，集合通過select轉匿名對象

List<DemoClass> liset = new List<DemoClass>(); 
DemoClass a0 = new DemoClass() { Id = 1, Name = "asd " };
DemoClass a1 = new DemoClass() { Id = 2, Name = "asd " }; 
liset.Add(a0);
liset.Add(a1);    

var ss = liset.Select((p) => new { newid = p.Id  }); //new {} 這樣的寫法創建匿名對象

還可以做出判斷或者轉換

var ss = liset.Select((p) => new { newid = p.Id, newName = p.Id.ToString() });

//就像這樣，想怎么玩都行

2,有些時候是把這個對象轉成另外的對象，以前的搞法就是循環，創建對象，給對象值賦值，對象集合添加，寫法的態繁瑣了

我們可以這么整

List<DemoClass> liset = new List<DemoClass>(); 
DemoClass a0 = new DemoClass() { Id = 1, Name = "asd " };
DemoClass a1 = new DemoClass() { Id = 2, Name = "asd " };
liset.Add(a0);
liset.Add(a1); 
List<pople> poples = liset.Select((p) => new pople { PID = p.Id, PName = p.Id.ToString() }).ToList(); 

//這樣就把 List<DemoClass> 集合值轉到 List<pople>集合了，至於里面的值怎么對應，自己注意類型和大小就可以了，同時也可以做篩選！看個人需要！
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原文鏈接：https://blog.csdn.net/weixin_42780928/java/article/details/91490348

3.select 出對象，cust 是一個Customer 對象

static void Main(string[] args)  
        {  
            List<Customer> customers = new List<Customer>()   
            {   
                new Customer("Jack", "Chen", "London"),  
                new Customer("Sunny","Peng", "Shenzhen"),  
                new Customer("Tom","Cat","London")  
            };  
            //使用IEnumerable<T>作為變量  
            var result =from cust in customers  
                        where cust.City == "London"  
                        select cust;  
            foreach (var item in result)  
            {  
                Console.WriteLine(item.FirstName+":"+item.City);  
            }  
            Console.Read();  
        }

4、 select 出對象的屬性字段 

var result =from cust in customerswhere cust.City == "London"  
            select cust.City 

多個屬性要用new ｛｝如下：

1. var result =from cust in customers where cust.City == "London"
2.  
               select new{cust.City,cust.FirstName};//new{}   匿名函數

5.重命名， city 和 name 是隨便起的

var result =from cust in customers where cust.City == "London"  
            select new{ city=cust.City, name ="姓名"+ cust.FirstName+""+cust.LastName };  
foreach (var item in result)  
{  
   Console.WriteLine(item.name+":"+item.city);  
}

6.直接實例化對象  //跟2有點相似

var result =from cust in customers where cust.City == "London"  
        select new Customer{ City = cust.City, FirstName = cust.FirstName }; 

7.selec 中嵌套select

var result =from cust in customers  where cust.City == "London"  
            select new{ city = cust.City,   
                        name=from cust1 in customers where cust1.City == "London"  
                        select cust1.LastName  
                      };