Find duplicates in List(Of String) in VB.NET

Question

I have a customers List(of String) on which I am trying to find the duplicate customers.

If Not customers.Count = customers.Distinct.ToList.Count Then
     customers = customers.Except(customers.Distinct.ToList)
End If

But I get the following exception:

InvalidCastException
Unable to cast object of type '<ExceptIterator>d__99`1[System.String]' to type
'System.Collections.Generic.List`1[System.String]'.

Is this the right way to find duplicates in a list?

Raj · Accepted Answer · 2012-06-27 15:09:30Z

11

customers = customers.GroupBy(Function(m) m) _
                 .Where(Function(g) g.Count() > 1) _
                 .Select(Function(g) g.Key).ToList

edited Jun 27, 2012 at 15:09

Raj

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answered Jun 27, 2012 at 14:45

Raphaël Althaus

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3 Comments

Raj Over a year ago

Thanks, but Except seems not removing the duplicates. Count of customers is 0 after this step. (customers.count = 581, customers.Distinct.ToList.count = 575)

Raphaël Althaus Over a year ago

@emaillenin yes, cause it's exactly what we try to do (which is not that smart, indeed). Look at my edit, maybe ?

Raj Over a year ago

I want to find the duplicates.. So subtracting the original list and the distinct list will give that.. Dont know how to subtract them..

Raj · Accepted Answer · 2012-06-27 15:12:59Z

10

The VB version:

Dim duplicates = listOfItems.GroupBy(Function(i) i)_
                            .Where(Function(g) g.Count() > 1)_
                            .[Select](Function(g) g.Key)

C#:

var duplicates = customers.GroupBy(x => x)
                          .Where(g => g.Count() > 1)
                          .Select(g => g.Key);

edited Jun 27, 2012 at 15:12

Raj

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answered Jun 27, 2012 at 14:59

ilivewithian

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