LINQ |如何找到给定序列的集合？

在LINQ中，您可以使用Aggregate方法创建自己的自定义聚合操作。此方法使您可以对集合或序列的值执行自定义聚合操作。它不支持C＃和VB.Net语言的查询语法，但可以支持两种语言的方法语法。它同时存在于Queryable和Enumerable类中。此方法以3种不同的方式重载：

1. Aggregate (IEnumerable ，TAccumulate，Func ，Func )：此方法用于在序列上应用累加器函数。指定的种子值用作初始累加器值，并且指定的函数用于选择结果值。
2. Aggregate (IEnumerable ，TAccumulate，Func )：此方法在序列上应用累加器函数。指定的种子值用作初始累加器值。
3. Aggregate (IEnumerable ，Func )：此方法在序列上应用累加器函数。

范例1：

// C# program to illustrate the
// use of aggregate method
using System;
using System.Linq;
  
class GFG {
  
    // Main Method
    static public void Main()
    {
  
        // Data source
        string[] sequence = {"Geeks", "gfg", 
                    "GeeksforGeeks", "GFG"};
  
        // Concatenate the element of the 
        // given sequence using Aggregate function
        var result = sequence.Aggregate((q1, q2) => q1 + "-" + q2);
        Console.WriteLine(result);
    }
}

输出：

Geeks-gfg-GeeksforGeeks-GFG

说明：在var结果中= sequence.Aggregate((q1，q2)=> q1 +“-” + q2); ，首先使用Geeks和gfg元素并在它们之间执行串联操作，然后使用此结果与GeeksfoGeeks元素进行串联。同样，此结果用于执行与GFG元素的连接操作，最后将最终结果存储在结果变量中。或者简单地就像： ((((Geeks-gfg)-GeeksforGeeks)-GFG)

范例2：

// C# program to find the total 
// salary of the employees
using System;
using System.Linq;
using System.Collections.Generic;
  
// Employee details
public class Employee {
  
    public int emp_id
    {
        get;
        set;
    }
  
    public string emp_name
    {
        get;
        set;
    }
  
    public string emp_gender
    {
        get;
        set;
    }
  
    public string emp_hire_date
    {
        get;
        set;
    }
  
    public int emp_salary
    {
        get;
        set;
    }
}
  
class GFG {
  
    // Main method
    static public void Main()
    {
        List emp = new List() {
  
            new Employee() {emp_id = 209, emp_name = "Anjita", emp_gender = "Female",
                                    emp_hire_date = "12/3/2017", emp_salary = 20000},
  
            new Employee() {emp_id = 210, emp_name = "Soniya", emp_gender = "Female",
                                    emp_hire_date = "22/4/2018", emp_salary = 30000},
  
            new Employee() {emp_id = 211, emp_name = "Rohit", emp_gender = "Male",
                                  emp_hire_date = "3/5/2016", emp_salary = 40000},
  
            new Employee() {emp_id = 212, emp_name = "Supriya", emp_gender = "Female",
                                      emp_hire_date = "4/8/2017", emp_salary = 40000},
  
            new Employee() {emp_id = 213, emp_name = "Anil", emp_gender = "Male",
                                emp_hire_date = "12/1/2016", emp_salary = 40000},
  
            new Employee() {emp_id = 214, emp_name = "Anju", emp_gender = "Female",
                                  emp_hire_date = "17/6/2015", emp_salary = 50000},
        };
  
        // Query to find the total salary
        // of the employees
        // Using Aggregate method
        var res = emp.Select(e => e.emp_salary).Aggregate((x,
                                                y) => x + y);
                                                  
        Console.WriteLine("Total salary of the Employees: {0}", res);
    }
}

输出：

Total salary of the Employees: 220000

说明：此var res中的Aggregate方法的工作= emp.Select(e => e.emp_salary).Aggregate((x，y)=> x + y);声明是：

(20000, 30000) => 20000 + 30000;
(50000, 40000) => 50000 + 40000;
(50000, 40000) => 130000 + 40000;
(130000, 40000) => 170000 + 40000;
(170000, 50000) => 170000 + 50000;
final value store in res is 220000

参考：

• https://docs.microsoft.com/zh-cn/dotnet/api/system.linq.enumerable.aggregate?view=netframework-4.8