LINQ介绍

參考：

LINQ查询主要运行操作包含：1）获取数据源；2）创建查询；3）运行查询。须要注意的是仅仅有在使用查询结果的时候才会去运行查询，或者在创建查询之后再加上tolist或者toarray之类的功能则能够马上运行。

// The Three Parts of a LINQ Query:         //  1. Data source.         int[] numbers = new int[7] { 0, 1, 2, 3, 4, 5, 6 };        // 2. Query creation.         // numQuery is an IEnumerable
      
                var numQuery =            from num in numbers            where (num % 2) == 0            select num;        // 3. Query execution.         foreach (int num in numQuery)        {            Console.Write("{0,1} ", num);        }
      

数据源能够来自于Array、List等或者直接从文件里读取的结果。

查询语句操作

參考：

Filter: where cust.City==”London” && cust.Name == “Devon”

Order: orderby cust.Name ascending

Group: group cust by cust.City into custGroup where custGroup.Count() > 2

Join: join dist in distributors on cust.City equals dist.City

其它功能

我们在使用LINQ操作的时候，往往另一些额外的需求，比方去重啊。分组啊等等。

// The Three Parts of a LINQ Query:             //  1. Data source.             int[] numbers = new int[] { 0, 1, 2, 3, 4, 5, 6, 4 };            // 2. Query creation.             // numQuery is an IEnumerable
      
                    var numQuery =                from num in numbers                where (num % 2) == 0                select num;            // 3. Query execution.             foreach (int num in numQuery.Distinct())            {                Console.WriteLine("{0,1} ", num);            }            foreach (var num in numQuery.GroupBy(key => key))            {                Console.WriteLine("{0}:{1} ", num.Key, num.Count());            }            foreach (int num in numQuery.GroupBy(key => key).Select(key => key.Key))            {                Console.WriteLine("{0,1} ", num);            }
      

并行处理

LINQ比較强大的是还提供了可并行处理的查询。这使得我们能够借助它来完毕一些查询或者处理的并行操作。

static void Main(string[] args)        {            // The Three Parts of a LINQ Query:             //  1. Data source.             int[] numbers = new int[100];            for (var i = 0; i < 100; i++)                numbers[i] = i;            // 2. Query creation.             // numQuery is an IEnumerable
      
                    var numQuery =                from num in numbers                where (num % 2) == 0                select num;            // 3. Query execution.             Split(numQuery.ToList(), 10)                .AsParallel()                .WithDegreeOfParallelism(3)                .Select(process)                .ToList();            Console.ReadKey();        }        static Tuple
       
        
         , int> process(Tuple
         
          
           , int> input)        {            foreach (var num in input.Item1)                Console.WriteLine("{0}-{1}", num, input.Item2);            return input;        }        static IEnumerable
           
            
             
              , int>> Split(List
              
                nums, int Count) { int index = 0; List
               
                 num = new List
                
                 (); foreach(var nm in nums) { num.Add(nm); if (num.Count >= Count) { yield return new Tuple
                 
                  
                   , int>(num, index++); num = new List
                   
                    (); } } if(num.Count > 0) { yield return new Tuple
                    
                     
                      , int>(num, index++); } }
                     
                    
                   
                  
                 
                
               
              
             
            
           
          
         
        
       
      

具体介绍能够參考：