What is the difference between the first and single functions in LINQ?

Question

Ravi Vishwakarma · Answer

First and Single operator difference 
First 
The collection has no element then throw NoElementsException. The first function returns the first row from or top one row from the collection.
The first method takes a condition to fetch elements from the collection 
Single 
The collection has no element then throw NoElementsException and the element has more than one then return MoreThanOneElementException.
The single function has checked the collection that element is single then return row.
The single method takes a condition but this condition allows one row, no more than one row.
Example
using System;
using System.Collections.Generic;
using System.Linq;
public class Program
{
and public static void Main()
and {
and  Listandlt;Student> students = new Listandlt;Student>(){
and  new Student() { StudentId = 1, Name = 'Ashu', Marks = 500 },
and  new Student() { StudentId = 2, Name = 'Shyam', Marks = 300 },
and  new Student() { StudentId = 3, Name = 'Shriyam', Marks = 400 },
and  new Student() { StudentId = 4, Name = 'Sunny', Marks = 550 },
and  new Student() { StudentId = 5, Name = 'Ram', Marks = 600 },
and  new Student() { StudentId = 6, Name = 'Krishna', Marks = 700 },
and  new Student() { StudentId = 7, Name = 'Anupam', Marks = 550 }
and  } ;
and  Student first = students.First();
and  Console.WriteLine('
First() :
');
and  Console.WriteLine('{0,-10} {1,10} {2,5}','Name', 'ID', 'Marks');
and  Console.WriteLine('{0,-10} {1,10} {2,5}', first.Name, first.StudentId, first.Marks);
and  // Student first = students.Where( stu => stu.Marks > 500).Single();
and  // this will throw an InvalidOperationException exception because more than 1 element in students.
and  Student last = students.Single( stu => stu.StudentId == 2);
and  Console.WriteLine('
Single() :
');
and  Console.WriteLine('{0,-10} {1,10} {2,5}','Name', 'ID', 'Marks');
and  Console.WriteLine('{0,-10} {1,10} {2,5}', last.Name, last.StudentId, last.Marks);
and  Console.ReadLine();
and }
}
class Student
{
public int StudentId { get; set; }
public string Name { get; set; }
public int Marks { get; set; }
}
Output
First() :
Name               ID MarksAshu                1   500
Single() :
Name               ID MarksShyam               2   300

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What is the difference between the first and single functions in LINQ?

Ethan Karla

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