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!
