Distinct Not Working With Linq to Objects

Distinct not working with LINQ to Objects

LINQ Distinct is not that smart when it comes to custom objects.

All it does is look at your list and see that it has two different objects (it doesn't care that they have the same values for the member fields).

One workaround is to implement the IEquatable interface as shown here.

If you modify your Author class like so it should work.

public class Author : IEquatable<Author>
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public bool Equals(Author other)
    {
        if (FirstName == other.FirstName && LastName == other.LastName)
            return true;

        return false;
    }

    public override int GetHashCode()
    {
        int hashFirstName = FirstName == null ? 0 : FirstName.GetHashCode();
        int hashLastName = LastName == null ? 0 : LastName.GetHashCode();

        return hashFirstName ^ hashLastName;
    }
}

Try it as DotNetFiddle

Not getting Distinct Items when using Linq to List?

Use

var queryResults = PatientList.GroupBy(x=>x.Id).Select(x=>x.FirstOrDefault())
    PatientList = queryResults.ToList<SelectListItem>();

You can always try

 PatientList = PatientList.GroupBy(x=>x.Id).Select(x=>x.FirstOrDefault()).ToList<SelectListItem>();

It will give you the distinct results based off whatever you group by

Check out http://blog.jordanterrell.com/post/LINQ-Distinct()-does-not-work-as-expected.aspx

Also another question for reference: Returning a Distinct IQueryable with LINQ?

Distinct not working with LINQ to Objects

LINQ Distinct is not that smart when it comes to custom objects.

All it does is look at your list and see that it has two different objects (it doesn't care that they have the same values for the member fields).

One workaround is to implement the IEquatable interface as shown here.

If you modify your Author class like so it should work.

public class Author : IEquatable<Author>
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public bool Equals(Author other)
    {
        if (FirstName == other.FirstName && LastName == other.LastName)
            return true;

        return false;
    }

    public override int GetHashCode()
    {
        int hashFirstName = FirstName == null ? 0 : FirstName.GetHashCode();
        int hashLastName = LastName == null ? 0 : LastName.GetHashCode();

        return hashFirstName ^ hashLastName;
    }
}

Try it as DotNetFiddle

ASP.net Core C# Linq Distinct not working

Your class ProcessListSummary probably does not override Equals and GetHashCode, so the default will be used from System.Object that just compares references. You use always a new instance of ProcessListSummary, so all are considered to be unequal.

So either override Equals+GetHashCode meaningfully, by comparing the relevant properties, and/or implement IEquatable<ProcessListSummary>(in the same way) or pass a custom IEqualityComparer<ProcessListSummary> to Distinct. The latter should be done if you have multiple ways to compare this class or you don't want to change (or can't change) it in general.

Another option is to use Distinct on an anonymous type or tuple which provide that feature:

PLDistinct = PL
    .Select(p => (p.Title,p.WSID,p.QImageTnURL,p.QImageURL,p.QDescription,p.PComplete,p.MIdent,p.WID))
    .Distinct()
    .Select(p => new ProcessListSummary {  Title=  p.Title, 
                                           WSID = p.WSID,
                                           QImageTnURL = p.QImageTnURL,
                                           QImageURL = p.QImageURL,
                                           QDescription = p.QDescription,
                                           PComplete= p.PComplete,
                                           MIdent = p.MIdent,
                                           WID = p.WID})
    .ToList();

Using Distinct with LINQ and Objects

I believe this post explains your problem:
http://blog.jordanterrell.com/post/LINQ-Distinct()-does-not-work-as-expected.aspx

The content of the above link can be summed up by saying that the Distinct() method can be replaced by doing the following.

var distinctItems = items
       .GroupBy(x => x.PropertyToCompare)
       .Select(x => x.First());

Distinct() on anonymous object not working in LINQ

You are using DateTime.Now for Created/Updated, so it would be quite unlikely that values between entries would be the same, they most likely differ by fraction of millisecond. If you displayed the values with greater precision, eg. .Ticks, they would be different.

I think you should save DateTime.Now to variable before LINQ and use it, to ensure they are the same for all entries. Other option is to add it to the object after .Distinct().

LINQ Distinct Not Working

You need to tell the Distinct method what equality comparer to use. I would also split that out into it's own class. For example:

Public Class TesteEqualityComparer 
    Implements IEqualityComparer(Of Teste)

    Public Function Equals2(x As Teste, y As Teste) As Boolean Implements IEqualityComparer(Of Teste).Equals
        Return x.Codigo = y.Codigo
    End Function

    Public Function GetHashCode1(obj As Teste) As Integer Implements IEqualityComparer(Of Teste).GetHashCode
        Return obj.Codigo.GetHashCode()
    End Function
End Class

And now your query is:

MsgBox(l.Distinct(New TesteEqualityComparer()).Count())

Linq Distinct not bringing back the correct results

So, you want to group them by Serial Number and retrieve the full DataRow? Assuming that after grouping them we want to retrieve the first item:

var distinctList = dt.AsEnumerable().GroupBy(a => a.Field<string>("SERIAL NUMBER"))
                       .Select(a => a.FirstOrDefault()).Distinct().ToList();

EDIT: As requested

var distinctValues = dt.AsEnumerable().Select(a => a.Field<string>("SERIAL NUMBER")).Distinct().ToList();
var duplicateValues = dt.AsEnumerable().GroupBy(a => a.Field<string>("SERIAL NUMBER")).SelectMany(a => a.Skip(1)).Distinct().ToList();
var duplicatesRemoved = dt.AsEnumerable().Except(duplicateValues);

Linq Distinct() is not working

use GroupBy instead of Distinct

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