How to use order by, group by in c#?

The OrderBy and GroupBy operators are essential LINQ methods in C# that allow you to sort and organize data collections. OrderBy sorts sequences in ascending order, while GroupBy organizes flat sequences into groups based on a specified key.

These operators are particularly useful when working with collections of objects that need to be organized or sorted for better data presentation and analysis.

Syntax

Following is the syntax for OrderBy operator −

var result = collection.OrderBy(x => x.PropertyName);
var resultDesc = collection.OrderByDescending(x => x.PropertyName);

Following is the syntax for GroupBy operator −

var result = collection.GroupBy(x => x.KeyProperty);

Using GroupBy Operator

The GroupBy operator organizes a flat sequence into groups based on a key selector. Each group contains items that share the same key value −

using System;
using System.Collections.Generic;
using System.Linq;

class ElectronicGoods {
   public int Id { get; set; }
   public string Name { get; set; }
   public string Category { get; set; }
   public static List<ElectronicGoods> GetElectronicItems() {
      return new List<ElectronicGoods>() {
         new ElectronicGoods { Id = 1, Name = "Mobile", Category = "Phone"},
         new ElectronicGoods { Id = 2, Name = "LandLine", Category = "Phone"},
         new ElectronicGoods { Id = 3, Name = "Television", Category = "TV"},
         new ElectronicGoods { Id = 4, Name = "Grinder", Category = "Food"},
         new ElectronicGoods { Id = 5, Name = "Mixer", Category = "Food"},
      };
   }
}

class Program {
   static void Main() {
      //Group by Category and order items within each group by Name
      var res = ElectronicGoods.GetElectronicItems().GroupBy(x => x.Category).Select(x => new {
         Key = x.Key,
         electronicGoods = x.OrderBy(c => c.Name)
      });
      
      foreach (var group in res) {
         Console.WriteLine("{0} - {1}", group.Key, group.electronicGoods.Count());
         Console.WriteLine("----------");
         foreach (var electronicGoods in group.electronicGoods) {
            Console.WriteLine(electronicGoods.Name + "\t" + electronicGoods.Category);
         }
         Console.WriteLine();
      }
   }
}

The output of the above code is −

Phone - 2
----------
LandLine	Phone
Mobile	Phone

TV - 1
----------
Television	TV

Food - 2
----------
Grinder	Food
Mixer	Food

Using OrderBy Operator

The OrderBy operator sorts the entire collection based on a specified property in ascending order −

using System;
using System.Collections.Generic;
using System.Linq;

class ElectronicGoods {
   public int Id { get; set; }
   public string Name { get; set; }
   public string Category { get; set; }
   public static List<ElectronicGoods> GetElectronicItems() {
      return new List<ElectronicGoods>() {
         new ElectronicGoods { Id = 1, Name = "Mobile", Category = "Phone"},
         new ElectronicGoods { Id = 2, Name = "LandLine", Category = "Phone"},
         new ElectronicGoods { Id = 3, Name = "Television", Category = "TV"},
         new ElectronicGoods { Id = 4, Name = "Grinder", Category = "Food"},
         new ElectronicGoods { Id = 5, Name = "Mixer", Category = "Food"},
      };
   }
}

class Program {
   static void Main() {
      //Order by Category in ascending order
      var res = ElectronicGoods.GetElectronicItems().OrderBy(x => x.Category);
      foreach (var items in res) {
         Console.WriteLine(items.Name + "\t" + items.Category);
      }
   }
}

The output of the above code is −

Grinder	Food
Mixer	Food
Mobile	Phone
LandLine	Phone
Television	TV

Using OrderByDescending

For descending order, use OrderByDescending method −

using System;
using System.Collections.Generic;
using System.Linq;

class Program {
   static void Main() {
      var numbers = new List<int> { 5, 2, 8, 1, 9, 3 };
      
      var ascending = numbers.OrderBy(x => x);
      var descending = numbers.OrderByDescending(x => x);
      
      Console.WriteLine("Ascending: " + string.Join(", ", ascending));
      Console.WriteLine("Descending: " + string.Join(", ", descending));
   }
}

The output of the above code is −

Ascending: 1, 2, 3, 5, 8, 9
Descending: 9, 8, 5, 3, 2, 1

Comparison

Conclusion

The OrderBy operator sorts collections in ascending order, while GroupBy organizes items into groups based on a key. Both operators can be combined to create sorted groups, making them powerful tools for data organization and presentation in C# applications.