Remove duplicates from a List in C#

Question

Anyone have a quick method for de-duplicating a generic List in C#?

Answer 1

Another way in .Net 2.0

    static void Main(string[] args)
    {
        List<string> alpha = new List<string>();

        for(char a = 'a'; a <= 'd'; a++)
        {
            alpha.Add(a.ToString());
            alpha.Add(a.ToString());
        }

        Console.WriteLine("Data :");
        alpha.ForEach(delegate(string t) { Console.WriteLine(t); });

        alpha.ForEach(delegate (string v)
                          {
                              if (alpha.FindAll(delegate(string t) { return t == v; }).Count > 1)
                                  alpha.Remove(v);
                          });

        Console.WriteLine("Unique Result :");
        alpha.ForEach(delegate(string t) { Console.WriteLine(t);});
        Console.ReadKey();
    }

Answer 2

I think the simplest way is:

Create a new list and add unique item.

Example:

        class MyList{
    int id;
    string date;
    string email;
    }
    
    List<MyList> ml = new Mylist();

ml.Add(new MyList(){
id = 1;
date = "2020/09/06";
email = "zarezadeh@gmailcom"
});

ml.Add(new MyList(){
id = 2;
date = "2020/09/01";
email = "zarezadeh@gmailcom"
});

 List<MyList> New_ml = new Mylist();

foreach (var item in ml)
                {
                    if (New_ml.Where(w => w.email == item.email).SingleOrDefault() == null)
                    {
                        New_ml.Add(new MyList()
                        {
                          id = item.id,
     date = item.date,
               email = item.email
                        });
                    }
                }

Answer 3

How about:

var noDupes = list.Distinct().ToList();

In .net 3.5?

Answer 4

You can use Union

obj2 = obj1.Union(obj1).ToList();

Answer 5

I like to use this command:

List<Store> myStoreList = Service.GetStoreListbyProvince(provinceId)
                                                 .GroupBy(s => s.City)
                                                 .Select(grp => grp.FirstOrDefault())
                                                 .OrderBy(s => s.City)
                                                 .ToList();

I have these fields in my list: Id, StoreName, City, PostalCode I wanted to show list of cities in a dropdown which has duplicate values. solution: Group by city then pick the first one for the list.

I hope it helps :)

Answer 6

If you're using .Net 3+, you can use Linq.

List<T> withDupes = LoadSomeData();
List<T> noDupes = withDupes.Distinct().ToList();