C# Program to Reverse the List of Cities using LINQ

In C#, LINQ (Language Integrated Query) is a powerful feature that allows us to perform queries on various data sources, including arrays, lists, and databases. It provides an efficient and concise way to manipulate data and has become an essential tool for developers. In this article, we will explore how to use LINQ to reverse a list of cities in C#.

LINQ is a set of extensions to the .NET Framework that provides a standard way to query data from different data sources using a common syntax. It allows developers to write queries that resemble SQL statements, making it easier to manipulate data in a more readable and concise way.

Syntax

Following is the syntax for using LINQ's Reverse() method

IEnumerable<T> reversedSequence = collection.Reverse();

For lists specifically, you can use

var reversedCities = cities.Reverse();  // Direct usage
var reversedCities = cities.AsEnumerable().Reverse();  // Explicit conversion

Using LINQ Reverse() Method

To reverse a list of cities using LINQ, we use the Reverse() extension method. This method creates a new sequence with the elements in reverse order without modifying the original collection

Example

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

class Program {
   static void Main() {
      List<string> cities = new List<string> {"New York", "Paris", "Tokyo", "London"};
   
      var reversedCities = cities.Reverse();
   
      Console.WriteLine("Original order:");
      foreach (var city in cities) {
         Console.WriteLine(city);
      }
      
      Console.WriteLine("\nReversed order:");
      foreach (var city in reversedCities) {
         Console.WriteLine(city);
      }
   }
}

The output of the above code is

Original order:
New York
Paris
Tokyo
London

Reversed order:
London
Tokyo
Paris
New York

Using ToList() with Reverse()

If you need to materialize the reversed sequence into a new list, you can chain the ToList() method

Example

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

class Program {
   static void Main() {
      List<string> cities = new List<string> {"Mumbai", "Delhi", "Bangalore", "Chennai"};
   
      List<string> reversedCityList = cities.Reverse().ToList();
   
      Console.WriteLine("Reversed cities as new List:");
      for (int i = 0; i < reversedCityList.Count; i++) {
         Console.WriteLine($"{i + 1}. {reversedCityList[i]}");
      }
   }
}

The output of the above code is

Reversed cities as new List:
1. Chennai
2. Bangalore
3. Delhi
4. Mumbai

Using Reverse() with Method Chaining

LINQ methods can be chained together for more complex operations. Here's an example that filters and reverses cities

Example

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

class Program {
   static void Main() {
      List<string> cities = new List<string> {"New York", "Paris", "Tokyo", "London", "Berlin", "Rome"};
   
      var filteredAndReversed = cities
         .Where(city => city.Length > 5)
         .Reverse();
   
      Console.WriteLine("Cities with more than 5 characters (reversed):");
      foreach (var city in filteredAndReversed) {
         Console.WriteLine(city);
      }
   }
}

The output of the above code is

Cities with more than 5 characters (reversed):
London
New York

Conclusion

LINQ's Reverse() method provides an efficient and readable way to reverse the order of elements in a collection. It creates a new sequence without modifying the original collection, making it perfect for functional programming approaches and method chaining scenarios in C#.