c# list make unique code example

Example 1: 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();
}

Example 2: 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).