Distinct in Linq

Sometimes, in .net it can get a bit confusing about which interface you need to implement for to get object equality to work correctly. When using the Distinct extension method in Linq, IEqualityComparer<T> is very useful

var items = new List<Cheese>();
items.Add(new Cheese { Name = "Cheddar" });	
items.Add(new Cheese { Name = "Cheddar" });	
items.Add(new Cheese { Name = "Red Leicester" });	
items.Add(new Cheese { Name = "Stilton" });	
var distinct = items.Distinct();	

foreach (var item in distinct) {	
    Console.WriteLine (item.Name);	
}

//outputs
// Cheddar
// Cheddar
// Red Leicester
// Stilton

The key part is implementing GetHashCode so that the two objects will return the same hash code.

An example implementation:

class CheeseNameComparer : IEqualityComparer<Cheese> {	

 public bool Equals (Cheese x, Cheese y)	{ 
  return x.Name == y.Name;		
 }

 public int GetHashCode (Cheese obj) {
  return obj.Name.GetHashCode();
 }
}

distinct = items.Distinct(new CheeseNameComparer());
foreach (var item in distinct) {
  Console.WriteLine (item.Name);
} 
//outputs
// Cheddar
// Red Leicester
// Stilton