LINQ - DISTINCT 单列和多列两种情况下的实现

单列:

 List<int> ages = new List<int> { 21, 46, 46, 55, 17, 21, 55, 55 };

            IEnumerable<int> distinctAges = ages.Distinct();

            Console.WriteLine("Distinct ages:");

            foreach (int age in distinctAges)
            {
                Console.WriteLine(age);
            }

            /*
             This code produces the following output:

             Distinct ages:
             21
             46
             55
             17
            */

多列:

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;
    }

}

Product[] products = { new Product { Name = "apple", Code = 9 }, 
                       new Product { Name = "orange", Code = 4 }, 
                       new Product { Name = "apple", Code = 9 }, 
                       new Product { Name = "lemon", Code = 12 } };

//Exclude duplicates.

IEnumerable<Product> noduplicates =
    products.Distinct(new ProductComparer());

foreach (var product in noduplicates)
    Console.WriteLine(product.Name + " " + product.Code);

/*
    This code produces the following output:
    apple 9 
    orange 4
    lemon 12
*/