LINQ |分区运算符|边走边走

在LINQ中，分区运算符用于将给定序列分为两部分，而无需对元素进行排序，并返回其中一部分。标准查询运算符支持4种不同类型的分区运算符：

1. 跳过
2. 跳过而
3. 拿
4. 边走边走

TakeWhile运算子

TakeWhile运算符用于满足给定条件的元素，只要它满足给定条件，并且当条件满足时，它会跳过那些不满足给定条件的元素。此方法以两种不同的方式重载：

• TakeWhile (IEnumerable ，Func )：只要指定条件为true，则此方法用于返回给定序列中的元素。
• TakeWhile (IEnumerable ，Func )：只要指定条件为true，则此方法用于返回给定序列中的元素。元素的索引值用于谓词函数的逻辑中。

重要事项：

• 它不支持C＃和VB.Net语言的查询语法。但是您可以使用TakeWhile方法查询变量，也可以将查询括在方括号中，然后调用TakeWhile方法。
• 它支持C＃和VB.Net语言的方法语法。
• 它同时存在于Queryable和Enumerable类中。
• 它是通过使用延迟执行来实现的。
• 如果源或条件为null，它将抛出ArgumentNullException。

范例1：

// C# program to illustrate the
// concept of TakeWhile operator
using System;
using System.Linq;
  
class GFG {
  
    static public void Main()
    {
  
        // Data source
        int[] sequence = {45, 67, 89, 13, 56,
                                76, 100, 90};
  
        // Query to pick those elements
        // which are less than 70
        // Using TakeWhile method
        var result = sequence.OrderBy(s => s).TakeWhile(s => s < 70);
  
        Console.WriteLine("New Sequence: ");
  
        // Display new sequence
        foreach(var val in result)
        {
            Console.WriteLine(val);
        }
    }
}

输出：

New Sequence: 
13
45
56
67

范例2：

// C# program to get the names of the 
// employees whose salary is less 
// than 50000
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;
    }
}
  
public 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 = "Anu", emp_gender = "Female",
                                  emp_hire_date = "4/8/2017", emp_salary = 80000},
  
            new Employee() {emp_id = 213, emp_name = "Anil", emp_gender = "Male",
                                emp_hire_date = "12/1/2016", emp_salary = 60000},
  
            new Employee() {emp_id = 214, emp_name = "Anju", emp_gender = "Female",
                                  emp_hire_date = "17/6/2015", emp_salary = 50000},
        };
  
        // Query to get the names of the
        // employees whose salary is less
        // than 50000 Using TakeWhile method
        var res = emp.TakeWhile(e => e.emp_salary < 50000);
  
        foreach(var val in res)
        {
            Console.WriteLine("Employee Name: {0}",
                                     val.emp_name);
        }
    }
}

输出：

Employee Name: Anjita
Employee Name: Soniya
Employee Name: Rohit