LINQ ToLookup()方法 LINQ函数|LINQ

本文概述

LINQ ToLookup运算符的语法
方法语法中的LINQ ToLookup()运算符示例
查询语法中的LINQ ToLookup()示例

【LINQ ToLookup()方法】LINQ中的ToLookup运算符是一种扩展方法, 用于从源中提取一组键/值对。在这里, 结果集合中的每个元素都是一个通用的Lookup对象。查找对象包含键和与键匹配的子序列项。
LINQ ToLookup运算符的语法这是使用LINQ ToLookup运算符将集合作为键/值对返回的语法。
C＃代码

var Emp = objEmployee.ToLookup(x => x.Department);

在以上语法中, 我们使用ToLookup运算符将” objEmployee” 的集合转换为键/值对列表。
方法语法中的LINQ ToLookup()运算符示例这是在方法语法中使用LINQ ToLookup()将输入集合项转换为键/值对列表的示例。
C＃代码

using System; using System.Collections; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace ConsoleApp1{class Program{static void Main(string[] args){//create an objEmployee of the class Employee and create a list of EmployeeList< Employee> objEmployee = new List< Employee> (){new Employee(){ Name="Akshay Tyagi", Department="IT", Country="India"}, new Employee(){ Name="Vaishali Tyagi", Department="Marketing", Country="Australia"}, new Employee(){ Name="Arpita Rai", Department="HR", Country="China"}, new Employee(){ Name="Shubham Ratogi", Department="Sales", Country="USA"}, new Employee(){ Name="Himanshu Tyagi", Department="Operations", Country="Canada"}}; //objEmployee.ToLookup() method is used to print the value of the data in the pair/collection of items.var Emp = objEmployee.ToLookup(x => x.Department); Console.WriteLine("Grouping Employees by Department"); Console.WriteLine("---------------------------------"); foreach (var KeyValurPair in Emp){Console.WriteLine(KeyValurPair.Key); // Lookup employees by Departmentforeach (var item in Emp[KeyValurPair.Key]){Console.WriteLine("\t" + item.Name + "\t" + item.Department + "\t" + item.Country); }}Console.ReadLine(); }}class Employee{public string Name { get; set; }public string Department { get; set; }public string Country { get; set; }}}

在上面的示例中, 我们使用ToLookup方法将Employee按部门分组。由于ToLookup会生成键/值对, 因此我们在foreach循环中使用了它, 而内部循环则根据作为输入传递的Key提取值。
输出

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查询语法中的LINQ ToLookup()示例

using System; using System.Collections; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace ConsoleApp1{class Program{static void Main(string[] args){List< Employee> objEmployee = new List< Employee> (){new Employee(){ Name="Ashish ", Department="Marketing", Country="India"}, new Employee(){ Name="John", Department="IT", Country="Australia"}, new Employee(){ Name="Kim", Department="Sales", Country="China"}, new Employee(){ Name="Marcia", Department="HR", Country="USA"}, new Employee(){ Name="John", Department="Operations", Country="Canada"}}; var emp = (from employee in objEmployee select employee).ToLookup(x => x.Department); Console.WriteLine("Grouping Employees by Department"); Console.WriteLine("---------------------------------"); foreach (var KeyValurPair in emp){Console.WriteLine(KeyValurPair.Key); // Lookup employees by Departmentforeach (var item in emp[KeyValurPair.Key]){Console.WriteLine("\t" + item.Name + "\t" + item.Department + "\t" + item.Country); }}Console.ReadLine(); }}class Employee{public string Name { get; set; }public string Department { get; set; }public string Country { get; set; }}}

输出