GroupBy By Multiple Keys in Linq

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GroupBy By Multiple Keys in Linq

In this article, I am going to discuss the GroupBy By Multiple Keys in Linq using C# with some examples. Please read our previous article before proceeding to this article where we discussed the Linq GroupBy Method in C# with examples in C#. As part of this article, we will discuss the following pointers.

1. Why do we need to group the data based on multiple keys?
2. How to use the Linq GroupBy Method with Multiple Keys in C#?
3. Examples using both Method and Query Syntax.

Why do we need to group the data based on Multiple keys?

In real-time applications, we need to group the data based on multiple keys. So in this article, we will see how to group the data based on multiple keys. But before that, you just need to remember one thing that when you are using multiple keys in Group By operator then the data returned is an anonymous type.

Student Helper Class:

We are going to use the following Student class. Please create a class with the name Student and then copy and paste the following code in it.

using System.Collections.Generic;
namespace GroupByDemo
{
    public class Student
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public string Gender { get; set; }
        public string Barnch { get; set; }
        public int Age { get; set; }

        public static List<Student> GetStudents()
        {
            return new List<Student>()
        {
            new Student { ID = 1001, Name = "Preety", Gender = "Female",
                                         Barnch = "CSE", Age = 20 },
            new Student { ID = 1002, Name = "Snurag", Gender = "Male",
                                         Barnch = "ETC", Age = 21  },
            new Student { ID = 1003, Name = "Pranaya", Gender = "Male",
                                         Barnch = "CSE", Age = 21  },
            new Student { ID = 1004, Name = "Anurag", Gender = "Male",
                                         Barnch = "CSE", Age = 20  },
            new Student { ID = 1005, Name = "Hina", Gender = "Female",
                                         Barnch = "ETC", Age = 20 },
            new Student { ID = 1006, Name = "Priyanka", Gender = "Female",
                                         Barnch = "CSE", Age = 21 },
            new Student { ID = 1007, Name = "santosh", Gender = "Male",
                                         Barnch = "CSE", Age = 22  },
            new Student { ID = 1008, Name = "Tina", Gender = "Female",
                                         Barnch = "CSE", Age = 20  },
            new Student { ID = 1009, Name = "Celina", Gender = "Female",
                                         Barnch = "ETC", Age = 22 },
            new Student { ID = 1010, Name = "Sambit", Gender = "Male",
                                         Barnch = "ETC", Age = 21 }
        };
        }
    }
}

Example: 

The following example group the students first by Branch and then by Gender. The student groups first sorted by Branch in descending order and then by Gender in ascending order. Finally, the students in each group are sorted by their names in ascending order. 

using System;
using System.Linq;
namespace GroupByDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            //Using Method Syntax
            var GroupByMultipleKeysMS = Student.GetStudents()
                                        .GroupBy(x => new { x.Barnch, x.Gender })
                                        .OrderByDescending(g => g.Key.Barnch).ThenBy(g => g.Key.Gender)
                                        .Select(g => new
                                        {
                                            Branch = g.Key.Barnch,
                                            Gender = g.Key.Gender,
                                            Students = g.OrderBy(x => x.Name)
                                        });
            //Using Query Syntax
            var GroupByMultipleKeysQS = from student in Student.GetStudents()
                                        group student by new
                                        {
                                            student.Barnch,
                                            student.Gender
                                        } into stdGroup
                                        orderby stdGroup.Key.Barnch descending,
                                                stdGroup.Key.Gender ascending
                                        select new
                                        {
                                            Branch = stdGroup.Key.Barnch,
                                            Gender = stdGroup.Key.Gender,
                                            Students = stdGroup.OrderBy(x => x.Name)
                                        };

            //It will iterate through each group
            foreach (var group in GroupByMultipleKeysQS)
            {
                Console.WriteLine($"Barnch : {group.Branch} Gender: {group.Gender} No of Students = {group.Students.Count()}");
                //It will iterate through each item of a group
                foreach (var student in group.Students)
                {
                    Console.WriteLine($"  ID: {student.ID}, Name: {student.Name}, Age: {student.Age} ");
                }
                Console.WriteLine();
            }
            Console.Read();
        }
    }
}

Output:

In the next article, I am going to discuss the Linq ToLookup Operator in C# with some examples. Here, in this article, I try to explain how to use the GroupBy By Multiple Keys in Linq with Examples. I hope you enjoy this article and understand the need and use of Linq GroupBy By Method with Multiple Keys.