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I have a list of objects declared in a class Toponyme implementing IEQuatable with four proprties City, CityGeoCode, County, State, Country.
I'm trying to remove the duplicates but without sucess.

What I have tried:

var liste = Liste.GroupBy(c => c.City + c.CityGeoCode + c.County + c.Region + c.Country).Select(c => c.First()).ToList();
and also

IEnumerable<toponyme> liste2 = Liste.Distinct().ToList();

Both without success.

Thanks for your help.
Updated 27-Aug-17 0:18am

1 solution

The way I'd do it is to use Distinct with a comparer:
public class MyClass
    public string Name { get; set; }
    public string Other { get; set; }
    public MyClass(string a, string b)
        Name = a; Other = b;
public class MyClassComp : IEqualityComparer<MyClass>
    public bool Equals(MyClass x, MyClass y)
        return x.Name == y.Name && x.Other == y.Other;

    public int GetHashCode(MyClass obj)
        if (Object.ReferenceEquals(obj, null)) return 0;
        int hashName = obj.Name == null ? 0 : obj.Name.GetHashCode();
        int hashOther = obj.Other == null ? 0 : obj.Other.GetHashCode();
        return hashName ^ hashOther;
I can then use that to do what you want:
List<MyClass> list = new List<MyClass>();
list.Add(new MyClass("A", "A"));
list.Add(new MyClass("A", "A"));
list.Add(new MyClass("A", "B"));
list.Add(new MyClass("A", "C"));
list.Add(new MyClass("B", "A"));
list.Add(new MyClass("B", "A"));
list.Add(new MyClass("B", "B"));
list.Add(new MyClass("B", "B"));
List<MyClass> newList = list.Distinct(new MyClassComp()).ToList();
Share this answer
Graeme_Grant 27-Aug-17 7:52am    
5'ed :)
BernardBouree 28-Aug-17 5:08am    
Thanks it works!
What about if I want to have the list of the duplicates?
OriginalGriff 28-Aug-17 5:28am    
That's where .Except comes in ... :laugh:
BernardBouree 28-Aug-17 13:07pm    
Well I don't know what is going on but it does not work any more.

Here is how I have implemented my comparison class

public class ToponymeGeoDbComp : IEqualityComparer<toponymegeodb>
public bool Equals(ToponymeGeoDb x, ToponymeGeoDb y)
return string.Equals(x.City.Trim(), y.City.Trim(), StringComparison.CurrentCultureIgnoreCase)
&& string.Equals(x.Country.Trim(), y.Country.Trim(), StringComparison.CurrentCultureIgnoreCase);

public int GetHashCode(ToponymeGeoDb obj)
if (ReferenceEquals(obj, null)) return 0;
var hashCodeCity = obj.City == null ? 0 : obj.City.GetHashCode();
var hashCodeCountry = obj.Country == null ? 0 : obj.Country.GetHashCode();
return hashCodeCity ^ hashCodeCountry;
And I'm calling it with
ToponymeGeoDb.ListeToponymesGeoDB = ToponymeGeoDb.ListeToponymesGeoDB.Distinct(new ToponymeGeoDbComp()).ToList();

Where ListeToponymesGeob is declared as static in my class ToponymeGeoDb.

When I try to trace I discover that the Equals method is never called .

Thnaks for the help.
OriginalGriff 28-Aug-17 14:05pm    
It does for me - copy'n'paste my code and you'll see - so you need to start by looking at the definition and content of ListeToponymesGeoDB immediately before your Distinct call is made.

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