Enumerable.Except(Of TSource) Method (IEnumerable(Of TSource), IEnumerable(Of TSource), IEqualityComparer(Of TSource))
The following example shows how to implement an equality comparer that can be used in the Except method.
public class Product
{
public string Name { get; set; }
public int Code { get; set; }
}
// Custom comparer for the Product class
class ProductComparer : IEqualityComparer<Product>
{
// Products are equal if their names and product numbers are equal.
public bool Equals(Product x, Product y)
{
//Check whether the compared objects reference the same data.
if (Object.ReferenceEquals(x, y)) return true;
//Check whether any of the compared objects is null.
if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
return false;
//Check whether the products’ properties are equal.
return x.Code == y.Code && x.Name == y.Name;
}
// If Equals() returns true for a pair of objects
// then GetHashCode() must return the same value for these objects.
public int GetHashCode(Product product)
{
//Check whether the object is null
if (Object.ReferenceEquals(product, null)) return 0;
//Get hash code for the Name field if it is not null.
int hashProductName = product.Name == null ? 0 : product.Name.GetHashCode();
//Get hash code for the Code field.
int hashProductCode = product.Code.GetHashCode();
//Calculate the hash code for the product.
return hashProductName ^ hashProductCode;
}
}
After you implement this comparer, you can use sequences of Product objects in the Except method, as shown in the following example.
Product[] fruits1 = { new Product { Name = "apple", Code = 9 },
new Product { Name = "orange", Code = 4 },
new Product { Name = "lemon", Code = 12 } };
Product[] fruits2 = { new Product { Name = "apple", Code = 9 } };
//Get all the elements from the first array
//except for the elements from the second array.
IEnumerable<Product> except =
fruits1.Except(fruits2, new ProductComparer());
foreach (var product in except)
Console.WriteLine(product.Name + " " + product.Code);
/*
This code produces the following output:
orange 4
lemon 12
*/
Reference:
mytechconnect 