C#：了解LINQ，简化数据查询和操作的强大工具(中）

var numbers = new List<int> { 1, 2, 3, 4, 5 };
var squares = numbers.Select(num => num * num);
// 执行结果：squares = { 1, 4, 9, 16, 25 }
var names = new List<string> { "Alice", "Bob", "Charlie" };
var nameLengths = names.Select(name => name.Length);
// 执行结果：nameLengths = { 5, 3, 7 }

var teams = new List<Team>
{
    new Team { Name = "Team A", Members = new List<string> { "Alice", "Bob" } },
    new Team { Name = "Team B", Members = new List<string> { "Charlie", "David" } },
    new Team { Name = "Team C", Members = new List<string> { "Eve", "Frank" } }
};
var allMembers = teams.SelectMany(team => team.Members);

"Alice", "Bob", "Charlie", "David", "Eve", "Frank"

var students = new List<Student>
{
    new Student { Name = "Alice", Grade = "A" },
    new Student { Name = "Bob", Grade = "B" },
    new Student { Name = "Charlie", Grade = "A" },
    new Student { Name = "David", Grade = "B" }
};
var groupedStudents = students.GroupBy(student => student.Grade);

foreach (var group in groupedStudents)
{
    Console.WriteLine("Grade: " + group.Key);
    foreach (var student in group)
    {
        Console.WriteLine("  " + student.Name);
    }
    Console.WriteLine();
}

Grade: A
  Alice
  Charlie
Grade: B
  Bob
  David

var customers = new List<Customer>
{
    new Customer { Id = 1, Name = "Alice" },
    new Customer { Id = 2, Name = "Bob" },
    new Customer { Id = 3, Name = "Charlie" }
};
var orders = new List<Order>
{
    new Order { OrderId = 1, CustomerId = 2, Product = "Phone" },
    new Order { OrderId = 2, CustomerId = 1, Product = "Laptop" },
    new Order { OrderId = 3, CustomerId = 2, Product = "Tablet" }
};
var result = customers.Join(
    orders,
    customer => customer.Id,
    order => order.CustomerId,
    (customer, order) => new { CustomerName = customer.Name, OrderProduct = order.Product });
foreach (var item in result)
{
    Console.WriteLine($"Customer: {item.CustomerName}, Product: {item.OrderProduct}");
}

Customer: Bob, Product: Phone
Customer: Alice, Product: Laptop
Customer: Bob, Product: Tablet

var departments = new List<Department>
{
    new Department { Id = 1, Name = "Sales" },
    new Department { Id = 2, Name = "Marketing" },
    new Department { Id = 3, Name = "IT" }
};
var employees = new List<Employee>
{
    new Employee { Id = 1, Name = "Alice", DepartmentId = 1 },
    new Employee { Id = 2, Name = "Bob", DepartmentId = 2 },
    new Employee { Id = 3, Name = "Charlie", DepartmentId = 1 },
    new Employee { Id = 4, Name = "David", DepartmentId = 3 },
    new Employee { Id = 5, Name = "Eve", DepartmentId = 2 }
};
var result = departments.GroupJoin(
    employees,
    department => department.Id,
    employee => employee.DepartmentId,
    (department, employeeGroup) => new { DepartmentName = department.Name, Employees = employeeGroup });
foreach (var item in result)
{
    Console.WriteLine($"Department: {item.DepartmentName}");
    foreach (var employee in item.Employees)
    {
        Console.WriteLine($"  Employee: {employee.Name}");
    }
    Console.WriteLine();
}

Department: Sales
  Employee: Alice
  Employee: Charlie
Department: Marketing
  Employee: Bob
  Employee: Eve
Department: IT
  Employee: David

var numbers = new List<int> { 1, 2, 3, 4, 5 };
var count = numbers.Count();
Console.WriteLine($"Count: {count}");

Count: 5

var numbers = new List<int> { 1, 2, 3, 4, 5 };
var sum = numbers.Sum();
Console.WriteLine($"Sum: {sum}");

Sum: 15

var prices = new List<double> { 10.5, 20.3, 15.2, 8.7 };
var total = prices.Sum();
Console.WriteLine($"Total: {total}");

Total: 54.7

var numbers = new List<int> { 10, 5, 3, 8, 2 };
var min = numbers.Min();
Console.WriteLine($"Min: {min}");

Min: 2

var prices = new List<double> { 10.5, 20.3, 15.2, 8.7 };
var minPrice = prices.Min();
Console.WriteLine($"Min Price: {minPrice}");

Min Price: 8.7

var numbers = new List<int> { 10, 5, 3, 8, 2 };
var max = numbers.Max();
Console.WriteLine($"Max: {max}");

Max: 10

var prices = new List<double> { 10.5, 20.3, 15.2, 8.7 };
var maxPrice = prices.Max();
Console.WriteLine($"Max Price: {maxPrice}");

Max Price: 20.3