Question

I have a code in VB.NET that I need to find duplicate items in a list of Invoice, with same number (amounts could be different), here is what I got to do but is not working, I don’t know if I should use LINQ maybe… the database is in txt file.

Public Class Invoice
  Public Property amount As Decimal
  Public Property number As String
  Public Property date As Date

  'extracting information from txt file

  Dim pesquisanotas As List(Of Invoice) = New NotaRepositorio().research()

‘part is not working, it is bringing invoices number with digits over 1 instead of repeated invoice numbers:

Dim DuplicateInvoice= From c In pesquisanotas
                                  Where (c.number.Count > 1)
                                  Select c

                    For Each item In DuplicateInvoice
                        MessageBox.Show(item.number)
                    Next

Answer 1

If the duplicates are already in the list, then this is how you can detect them:

Class DemoClass
  Public Property amount As Decimal
  Public Property number As String
  Public Property [date] As Date
End Class

Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click
  Dim lstSource As New List(Of DemoClass)
  lstSource.Add(New DemoClass With {.amount = 121, .number = "121", .date = #1/1/2012#})
  lstSource.Add(New DemoClass With {.amount = 122, .number = "122", .date = #1/2/2012#})
  lstSource.Add(New DemoClass With {.amount = 123, .number = "123", .date = #1/3/2012#})
  lstSource.Add(New DemoClass With {.amount = 124, .number = "124", .date = #1/4/2012#})
  lstSource.Add(New DemoClass With {.amount = 125, .number = "125", .date = #1/5/2012#})
  lstSource.Add(New DemoClass With {.amount = 126, .number = "126", .date = #1/6/2012#})
  lstSource.Add(New DemoClass With {.amount = 127, .number = "127", .date = #1/7/2012#})
  lstSource.Add(New DemoClass With {.amount = 128, .number = "123", .date = #1/8/2012#}) 'dup'
  lstSource.Add(New DemoClass With {.amount = 129, .number = "129", .date = #1/9/2012#})
  lstSource.Add(New DemoClass With {.amount = 130, .number = "130", .date = #1/10/2012#})
  lstSource.Add(New DemoClass With {.amount = 131, .number = "122", .date = #1/11/2012#}) 'dup'
  lstSource.Add(New DemoClass With {.amount = 132, .number = "132", .date = #1/12/2012#})

  For intOuter As Integer = 0 To lstSource.Count - 2
    For intInner As Integer = intOuter + 1 To lstSource.Count - 1
      If lstSource(intOuter).number = lstSource(intInner).number Then
        'duplicate found
        MsgBox("Duplicate found: " & lstSource(intOuter).number)
      End If
    Next intInner
  Next intOuter
End Sub