LINQ GroupBy Query

Here are some common LINQ queries related to GroupBy, demonstrating how to group data by specific criteria and perform aggregations or transformations on those groups:

1. Basic Group By

Group items by a single key and select the groups.

var employees = new List<Employee>
{
    new Employee { Department = "HR", Name = "Rohatash" },
    new Employee { Department = "IT", Name = "Mohit" },
    new Employee { Department = "HR", Name = "Jeet" }
};

var groupedByDepartment = from emp in employees
                          group emp by emp.Department into departmentGroup
                          select new
                          {
                              Department = departmentGroup.Key,
                              Employees = departmentGroup.ToList()
                          };

// Output: { Department = "HR", Employees = [{ Name = "Rohatash" }, { Name = "Jeet" }] },
//         { Department = "IT", Employees = [{ Name = "Mohit" }] }

2. Group By with Aggregation

Group items and compute aggregate values for each group.

var orders = new List<Order>
{
    new Order { Category = "Electronics", Amount = 100 },
    new Order { Category = "Clothing", Amount = 50 },
    new Order { Category = "Electronics", Amount = 150 },
    new Order { Category = "Clothing", Amount = 75 }
};

var totalSalesByCategory = from order in orders
                           group order by order.Category into categoryGroup
                           select new
                           {
                               Category = categoryGroup.Key,
                               TotalSales = categoryGroup.Sum(o => o.Amount)
                           };

// Output: { Category = "Electronics", TotalSales = 250 },
//         { Category = "Clothing", TotalSales = 125 }

3. Group By with Filtering

Group items and then filter the results within each group.

var employees = new List<Employee>
{
    new Employee { Department = "HR", Name = "Alice", Salary = 60000 },
    new Employee { Department = "IT", Name = "Bob", Salary = 50000 },
    new Employee { Department = "HR", Name = "Charlie", Salary = 70000 },
    new Employee { Department = "IT", Name = "David", Salary = 55000 }
};

var highEarnersByDepartment = from emp in employees
                              group emp by emp.Department into departmentGroup
                              let highEarners = departmentGroup.Where(e => e.Salary > 55000)
                              where highEarners.Any()
                              select new
                              {
                                  Department = departmentGroup.Key,
                                  HighEarners = highEarners.ToList()
                              };

// Output: { Department = "HR", HighEarners = [{ Name = "Charlie", Salary = 70000 }] },
//         { Department = "IT", HighEarners = [{ Name = "David", Salary = 55000 }] }