how to use LINQ Conversion Operators in C#?

Ethan Karla 1021 24 Sep 2021

how to use LINQ Conversion Operators (ToList, ToArray, ToLookup, Cast, OfType) in SQL data and normal data?

Ask by Ethan Karla

Updated 24 Sep 2021

1 Answers

Ravi Vishwakarma 27 Sep 2021 Accepted Answer

Conversion Operators are used to converting elements in a list or collection. There are many types of conversion operators in LINQ.

There is the following Conversion Operator.

ToList - it converts collection to list format
ToArray - it converts collection to array format
ToLookup - It converts group of elements into Lookup<tkey, telement>
CAST - It converts non-generic list to generic list (IEnumerable to IEnumerable)
OFTYPE - It is used to filters collection based on specified type
ASENUMERABLE - It is used to convert input elements as IEnumerable
ASQUERYABLE - It converts IEnumerable to IQueryable
ToDictionary - It converts input elements into dictionary based on key selector function

Example

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

public class Program
{

 public static void Main()
 {
  List<Student> students = new List<Student>()
  {
  new Student() { StudentId = 1, Name = 'Ashu', Marks = 500 },
  new Student() { StudentId = 2, Name = 'Shyam', Marks = 300 },
  new Student() { StudentId = 3, Name = 'Shriyam', Marks = 400 },
  new Student() { StudentId = 4, Name = 'Sunny', Marks = 550 },
  new Student() { StudentId = 5, Name = 'Ram', Marks = 600 },
  new Student() { StudentId = 6, Name = 'Krishna', Marks = 700 },
  new Student() { StudentId = 7, Name = 'Anupam', Marks = 550 }
  };

  List<Student> list = students.Where( stu => stu.Marks > 500).ToList();

  Console.WriteLine('\nToList() :\n');
  Console.WriteLine('{0,-10} {1,10} {2,5}','Name', 'ID', 'Marks');
  list.ForEach(item => Console.WriteLine('{0,-10} {1,10} {2,5}', item.Name, item.StudentId, item.Marks) );

  Student[] studentAry = students.Where( stu => stu.Name.StartsWith('A')).ToArray();

  Console.WriteLine('\nToArray() :\n');
  Console.WriteLine('{0,-10} {1,10} {2,5}','Name', 'ID', 'Marks');
  foreach(Student stu in studentAry)
   Console.WriteLine('{0,-10} {1,10} {2,5}', stu.Name, stu.StudentId, stu.Marks);

  IEnumerable<Student> enumerable = students.Where( stu => stu.Marks < 500).AsEnumerable();

  Console.WriteLine('\nAsEnumerable() :\n');
  Console.WriteLine('{0,-10} {1,10} {2,5}','Name', 'ID', 'Marks');
  foreach( Student student in enumerable)
   Console.WriteLine('{0,-10} {1,10} {2,5}', student.Name, student.StudentId, student.Marks);

  IQueryable<Student> queryable = students.Where( stu => stu.StudentId < 5).AsQueryable();

  Console.WriteLine('\nAsQueryable() :\n');
  Console.WriteLine('{0,-10} {1,10} {2,5}','Name', 'ID', 'Marks');
  foreach( Student student in queryable)
   Console.WriteLine('{0,-10} {1,10} {2,5}', student.Name, student.StudentId, student.Marks);

  Dictionary<int, string> dictionary = students.Where( stu => stu.StudentId < 5).ToDictionary(stu => stu.StudentId, stu => stu.Name);

  Console.WriteLine('\nToDictionary() :\n');
  Console.WriteLine('{0,-3} {1,-10}','ID', 'Marks');
  foreach( var student in dictionary)
   Console.WriteLine('{0,-3} {1,-10}', student.Key, student.Value);

  Console.ReadLine();

 }

}

class Student
{
public int StudentId { get; set; }
public string Name { get; set; }
public int Marks { get; set; }
}

OUtput

ToList() :

Name               ID Marks
Sunny               4   550
Ram                 5   600
Krishna             6   700
Anupam              7   550

ToArray() :

Name               ID Marks
Ashu                1   500
Anupam              7   550

AsEnumerable() :

Name               ID Marks
Shyam               2   300
Shriyam             3   400

AsQueryable() :

Name               ID Marks
Ashu                1   500
Shyam               2   300
Shriyam             3   400
Sunny               4   550

ToDictionary() :
ID  Marks     
1   Ashu      
2   Shyam     
3   Shriyam   
4   Sunny

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