csharp_linq

gistfile1.txt

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;

public class Book
{
    public string Region { get; set; }
    public double AUM { get; set; }
}

public class Student
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Course
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int TeacherId { get; set; }
}

public class Teacher
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Grade
{
    public int StudentId { get; set; }
    public int CourseId { get; set; }
    public int GradeValue { get; set; }
}


class Program {
    static void Main(string[] args) {
        IList<int> nums = new List<int> { 1, 3, 5, 7, 9, 11, 13, 15, 17 };
        var smallNums = from num in nums
        where num < 10
        select num;
        nums.Add(2);
        int countSmallNums = smallNums.Count(); // Answer is 6, not 5. LINQ Lazy Evaluates!

        // Filtering
        var numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
        var evenNumbers = numbers.Where(n => n % 2 == 0);
        foreach (var number in evenNumbers)
        {
            Console.WriteLine(number); // Output: 2, 4, 6, 8, 10
        }

        // Projection
        var names = new List<string> { "John", "Jane", "Doe", "Alice" };
        var nameLengths = names.Select(name => name.Length);
        foreach (var length in nameLengths)
        {
            Console.WriteLine(length); // Output: 4, 4, 3, 5
        }

        // Sorting
        var unsortedNumbers = new List<int> { 5, 3, 8, 1, 2, 7, 4, 6 };
        var sortedNumbers = unsortedNumbers.OrderBy(n => n);
        foreach (var number in sortedNumbers)
        {
            Console.WriteLine(number); // Output: 1, 2, 3, 4, 5, 6, 7, 8
        }

        // Aggregation
        var numbers2 = new List<int> { 1, 2, 3, 4, 5 };
        var sum = numbers2.Sum();
        Console.WriteLine(sum); // Output: 15

        var books = new List<Book>
        {
            new Book { Region = "APAC", AUM = 1000000 },
            new Book { Region = "EMEA", AUM = 1500000 },
            new Book { Region = "AMER", AUM = 2000000 },
            new Book { Region = "APAC", AUM = 1200000 },
            new Book { Region = "EMEA", AUM = 1800000 },
            new Book { Region = "AMER", AUM = 2200000 }
        };

        // Anonymous Type
        var groupedAUM = books.GroupBy(book => book.Region)
                              .Select(group => new
                              {
                                  Region = group.Key,
                                  TotalAUM = group.Sum(book => book.AUM)
                              });

        foreach (var item in groupedAUM)
        {
            Console.WriteLine($"Region: {item.Region}, Total AUM: {item.TotalAUM}");
        }


        // Joining
        var students = new List<Student>
        {
            new Student { Id = 1, Name = "John" },
            new Student { Id = 2, Name = "Jane" },
            new Student { Id = 3, Name = "Doe" }
        };

        var courses = new List<Course>
        {
            new Course { Id = 1, Name = "Math", TeacherId = 1 },
            new Course { Id = 2, Name = "Physics", TeacherId = 2 }
        };

        var teachers = new List<Teacher>
        {
            new Teacher { Id = 1, Name = "Mr. Smith" },
            new Teacher { Id = 2, Name = "Mrs. Johnson" }
        };

        var grades = new List<Grade>
        {
            new Grade { StudentId = 1, CourseId = 1, GradeValue = 85 },
            new Grade { StudentId = 2, CourseId = 1, GradeValue = 90 },
            new Grade { StudentId = 3, CourseId = 1, GradeValue = 80 },
            new Grade { StudentId = 1, CourseId = 2, GradeValue = 88 },
            new Grade { StudentId = 2, CourseId = 2, GradeValue = 92 },
            new Grade { StudentId = 3, CourseId = 2, GradeValue = 85 }
        };
        
        var result = from student in students
                     join grade in grades.Where(g => g.GradeValue>=80)
                     on student.Id equals grade.StudentId
                     join course in courses
                     on new { Name = "Math", CourseId = grade.CourseId } equals new { course.Name, CourseId = course.Id }
                     join teacher in teachers
                     on course.TeacherId equals teacher.Id
                     select new
                     {
                         student.Name,
                         CourseName = course.Name,
                         grade.GradeValue,
                         TeacherName = teacher.Name
                     };

        foreach (var item in result)
        {
            Console.WriteLine($"{item.Name} scored {item.GradeValue} in {item.CourseName} taught by {item.TeacherName}");
        }

    }
}