Recently I was working with data from a generic List<T> and one of my objectives is to get the distinct values that is found in the List. Consider that we have this simple class that holds the following properties: public class Product
{
public
string Make { get; set; }
public
string Model { get; set; }
}
Now in the page code behind we will create a list of product by doing the following:
private List<Product> GetProducts() {
List<Product> products = new List<Product>();
Product p = new Product();
p.Make = "Samsung";
p.Model = "Galaxy S 1";
products.Add(p);
p = new Product();
p.Make = "Samsung";
p.Model = "Galaxy S 2";
products.Add(p);
p = new Product();
p.Make = "Samsung";
p.Model = "Galaxy Note";
products.Add(p);
p = new Product();
p.Make = "Apple";
p.Model = "iPhone 4";
products.Add(p);
p = new Product();
p.Make = "Apple";
p.Model = "iPhone 4s";
products.Add(p);
p = new Product();
p.Make = "HTC";
p.Model = "Sensation";
products.Add(p);
p = new Product();
p.Make = "HTC";
p.Model = "Desire";
products.Add(p);
p = new Product();
p.Make = "Nokia";
p.Model = "Some Model";
products.Add(p);
p = new Product();
p.Make = "Nokia";
p.Model = "Some Model";
products.Add(p);
p = new Product();
p.Make = "Sony Ericsson";
p.Model = "800i";
products.Add(p);
p = new Product();
p.Make = "Sony Ericsson";
p.Model = "800i";
products.Add(p);
return products;
}
And then let’s bind the products to the GridView.
protected void Page_Load(object sender, EventArgs e) {
if (!IsPostBack) {
Gridview1.DataSource = GetProducts();
Gridview1.DataBind();
}
}
Running the code will display something like this in the page:
Now what I want is to get the distinct row values from the list. So what I did is to use the LINQ Distinct operator and unfortunately it doesn'
t work. In order for it work is you must use the overload method of the Distinct operator for you to get the desired results. So I’ve added this IEqualityComparer<T> class to compare values:
class ProductComparer : IEqualityComparer<Product>
{
public bool Equals(Product x, Product y) {
if (Object.ReferenceEquals(x, y)) return true;
if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
return false;
return x.Make == y.Make && x.Model == y.Model;
}
public int GetHashCode(Product product) {
if (Object.ReferenceEquals(product, null)) return 0;
int hashProductName = product.Make == null ? 0 : product.Make.GetHashCode();
int hashProductCode = product.Model.GetHashCode();
return hashProductName ^ hashProductCode;
}
}
After that you can then bind the GridView like this:
protected void Page_Load(object sender, EventArgs e) {
if (!IsPostBack) {
Gridview1.DataSource = GetProducts().Distinct(new ProductComparer());
Gridview1.DataBind();
}
}
Running the page will give you the desired output below:
As you notice, it now eliminates the duplicate rows in the GridView. Now what if we only want to get the distinct values for a certain field. For example I want to get the distinct “Make” values such as Samsung, Apple, HTC, Nokia and Sony Ericsson and populate them to a DropDownList control for filtering purposes. I was hoping the the Distinct operator has an overload that can compare values based on the property value like (GetProducts().Distinct(o => o.PropertyToCompare). But unfortunately it doesn’t provide that overload so what I did as a workaround is to use the GroupBy,Select and First LINQ query operators to achieve what I want.
Here’s the code to get the distinct values of a certain field.
protected void Page_Load(object sender, EventArgs e) {
if (!IsPostBack) {
DropDownList1.DataSource = GetProducts().GroupBy(o => o.Make).Select(o => o.First());
DropDownList1.DataTextField = "Make";
DropDownList1.DataValueField = "Model";
DropDownList1.DataBind();
}
}
Running the code will display the following output below:
That’s it! I hope someone find this post useful!
