Except C# with Example

The Except method returns the set of items which are contained in the first collection but are not contained in the 
second. The default IEqualityComparer is used to compare the items within the two sets. There is an overload 
which accepts an IEqualityComparer as an argument. 
Example: 
int[] first = { 1, 2, 3, 4 }; 
int[] second = { 0, 2, 3, 5 }; 
IEnumerable inFirstButNotInSecond = first.Except(second); 
// inFirstButNotInSecond = { 1, 4 } 
Output: 
1 
4 
Live Demo on .NET Fiddle 
In this case .Except(second) excludes elements contained in the array second, namely 2 and 3 (0 and 5 are not 
contained in the first array and are skipped). 
 

Note that Except implies Distinct (i.e., it removes repeated elements). For example: 
int[] third = { 1, 1, 1, 2, 3, 4 }; 
IEnumerable inThirdButNotInSecond = third.Except(second); 
// inThirdButNotInSecond = { 1, 4 } 
Output: 
1 
4 
Live Demo on .NET Fiddle 
In this case, the elements 1 and 4 are returned only once. 
Implementing IEquatable or providing the function an IEqualityComparer will allow using a different method to 
compare the elements. Note that the GetHashCode method should also be overridden so that it will return an 
identical hash code for object that are identical according to the IEquatable implementation. 
Example With IEquatable: 
class Holiday : IEquatable 
{ 
public string Name { get; set; } 
public bool Equals(Holiday other) 
{ 
return Name == other.Name; 
} 
// GetHashCode must return true whenever Equals returns true. 
public override int GetHashCode() 
{ 
//Get hash code for the Name field if it is not null. 
return Name?.GetHashCode() ?? 0; 
} 
} 
public class Program 
{ 
public static void Main() 
{ 
List holidayDifference = new List(); 
List remoteHolidays = new List 
{ 
new Holiday { Name = "Xmas" }, 
new Holiday { Name = "Hanukkah" }, 
new Holiday { Name = "Ramadan" } 
}; 
List localHolidays = new List 
{ 
new Holiday { Name = "Xmas" }, 
new Holiday { Name = "Ramadan" } 
}; 
 

holidayDifference = remoteHolidays 
.Except(localHolidays) 
.ToList(); 
holidayDifference.ForEach(x => Console.WriteLine(x.Name)); 
} 
} 
Output: 
Hanukkah 
Live Demo on .NET Fiddle