Remove duplicates object in a list

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Hi
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.

Posted 26-Aug-17 23:57pm

BernardBouree

Updated 27-Aug-17 0:18am

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OriginalGriff · Accepted Answer · 2017-08-27T00:18:00

Solution 1

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();

Posted 27-Aug-17 0:18am

OriginalGriff

Comments

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.