C# Linq+ValueTuple(元祖)，成为Linq高手！

前言

Linq是C# 最强语法之一，和委托,get set并列(在我的心中)。我很早就听说了Linq 很牛了，这里来了解一下Linq如何写代码

C# Linq详解

C# 元祖，最佳的临时变量。

简单使用:能被2整除

static void Main(string[] args)
{
    int[] numbers = new int[7] { 0, 1, 2, 3, 4, 5, 6 };
    //选择能被2整除的数
    var numLinq = from item1 in numbers 
                  where item1 %2 == 0
                  select item1;
	
    Console.WriteLine(JsonConvert.SerializeObject(numLinq));
	//[0,2,4,6]
	
    Console.WriteLine("Hello, World!");

    Console.ReadKey();
}

这里简单说明一下基础语法：

• from item in source:item临时变量，source数据源
• where:临时变量成立条件
• select:返回值

ValueTuple使用:两数相加等于4

不使用元祖

        static void Main(string[] args)
        {
            int[] numbers = new int[7] { 0, 1, 2, 3, 4, 5, 6 };
            //选择两数相加等于4的
            var numLinq = from item1 in numbers from item2 in numbers
                          where item1 + item2 == 4
                          select new int[] { item1,item2};

            Console.WriteLine(JsonConvert.SerializeObject(numLinq));

            Console.WriteLine("Hello, World!");

            Console.ReadKey();
        }

使用元祖

static void Main(string[] args)
   {
       int[] numbers = new int[7] { 0, 1, 2, 3, 4, 5, 6 };
       //选择两数相加等于4的
       var numLinq = from item1 in numbers from item2 in numbers
                     where item1 + item2 == 4
                     select (item1,item2);

       Console.WriteLine(JsonConvert.SerializeObject(numLinq));

       Console.WriteLine("Hello, World!");

       Console.ReadKey();
   }

结果：

[{"Item1":0,"Item2":4},{"Item1":1,"Item2":3},{"Item1":2,"Item2":2},{"Item1":3,"Item2":1},{"Item1":4,"Item2":0}]

排序

• orderby ascending:升序
• orderby descending:降序

static void Main(string[] args)
{
    int[] numbers = new int[] { 1,6,4,0,3,4,6,7,5 };
    //升序
    var numLinq = from item1 in numbers 
                  orderby item1 ascending
                  select item1;

    Console.WriteLine(JsonConvert.SerializeObject(numLinq));

    //降序
    var numLinq2 = from item1 in numbers
                  orderby item1 descending
                  select item1;

    Console.WriteLine(JsonConvert.SerializeObject(numLinq2));

    Console.WriteLine("Hello, World!");

    Console.ReadKey();
}

基于类的Linq

我们这里新建一个Person类

 public class Person
 {
     public string Name { get; set; }

     public int Id { get; set; }
 }

GroupBy

static void Main(string[] args)
{
    var persons = new List<Person>() {
        new Person(){Name = "小王",Id = 1},
        new Person(){Name = "小红",Id=2},
        new Person(){Name = "小黑", Id=2},
    };

    //使用聚合函数，返回的是分类好的数组
    var res = from item in persons
              group item by item.Id;
    
    Console.WriteLine(JsonConvert.SerializeObject(res));

    Console.WriteLine("Hello, World!");

    Console.ReadKey();
}

Join

join + in是两集合聚合，聚合条件必须要用equals，不能用=

static void Main(string[] args)
{
    var person1 = new List<Person>() {
        new Person(){Name = "小王",Id = 1},
        new Person(){Name = "小红",Id=2},
    };

    var person2 = new List<Person>() {
        new Person(){Name = "小拉",Id = 1},
        new Person(){Name = "小辣",Id=2},
    };

    //将相同ID的名称拼接
    var res = from item1 in person1
              join item2 in person2 on item1.Id  equals item2.Id
              select new Person() { Name = item1.Name+item2.Name,Id = item1.Id};

    
    Console.WriteLine(JsonConvert.SerializeObject(res));

    Console.WriteLine("Hello, World!");

    Console.ReadKey();
}

Distinct去重

普通去重

 static void Main(string[] args)
   {
       var lists = new List<int>() {1,2,3,4,5,5,5,6,1,2 };
       
       //普通去重
       var res = from item in lists.Distinct() select item;    
       
       Console.WriteLine(JsonConvert.SerializeObject(res));

       Console.WriteLine("Hello, World!");

       Console.ReadKey();
   }

选择去重

 static void Main(string[] args)
 {
     var lists = new List<Person>() {
         new Person(){Name= "小王",Id= 1},
         new Person(){Name = "小丽" ,Id=2},
         new Person(){Name = "小乐",Id = 2},
     };

     //普通去重
     var res = from item in lists.DistinctBy(x => x.Id)
               select item;

     Console.WriteLine(JsonConvert.SerializeObject(res));

     Console.WriteLine("Hello, World!");

     Console.ReadKey();
 }

集合去重

Except

static void Main(string[] args)
{
    var list1 = new int[] { 1, 2, 3, 4, 5 };
    var list2 = new int[] { 3, 4, 5, 6, 7 };

    var res = from item in list1.Except(list2).ToList()
              select item;

    Console.WriteLine("list1去掉list2重复的");
    Console.WriteLine(JsonConvert.SerializeObject(res));

    Console.WriteLine("Hello, World!");

    Console.ReadKey();
}

Intersect

static void Main(string[] args)
{
    var list1 = new int[] { 1, 2, 3, 4, 5 };
    var list2 = new int[] { 3, 4, 5, 6, 7 };

    var res = from item in list1.Intersect(list2)
              select item;

    Console.WriteLine("list1拿到list2重复的");
    Console.WriteLine(JsonConvert.SerializeObject(res));

    Console.WriteLine("Hello, World!");

    Console.ReadKey();
}

Union

static void Main(string[] args)
{
    var list1 = new int[] { 1, 2, 3, 4, 5 };
    var list2 = new int[] { 3, 4, 5, 6, 7 };

    var res = from item in list1.Union(list2)
              select item;

    Console.WriteLine("list1和list2的并集");
    Console.WriteLine(JsonConvert.SerializeObject(res));

    Console.WriteLine("Hello, World!");

    Console.ReadKey();
}

总结

我这里只是简单的使用了一下Linq，如果想详细了解，可以去看看这个文章，写的确实是非常的全面

C# Linq详解