CSHARP

unique items in list c#

var uniqueItemsList = yourList.Distinct().ToList();

how to get unique list in c#

using(var dataModel = new DataModel())
{
  var classes = dataModel.Attributes.Where(a => a.Field == "Class").Select(a => a.Key).Distinct().ToList();
}

C# list of unique items

HashSet<T> uniqueList;

c# list with only unique items

If your requirements are to have no duplicates, you should be using a HashSet.
HashSet.Add will return false when the item already exists (if that even matters to you).