Question

我在VB.NET中有一个代码，我需要在发票列表中找到重复的项目，具有相同的编号（数量可能不同），这是我要做的但是不工作，我不知道我是否应该使用LINQ ...数据库在txt文件中。

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()

'部分不起作用，它带有数字超过1的发票号码，而不是重复的发票号码：

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

如果重复项已经在列表中，那么您就可以检测它们了：

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

Answer 2

您需要使用GroupBy（）函数。 VB不是我的语言，所以我会尽力翻译。

Dim invoice = From c In pesquisanotas
                Group c By c.number Into g
                Where (g.Count > 1)
                Select g.Key

Answer 3

实施自定义IEquatable(Of T)并使用List(Of T).Contains功能来防止添加重复项：

Class DemoClass
  Implements IEquatable(Of DemoClass)

  Public Property amount As Decimal
  Public Property number As String
  Public Property [date] As Date

  Public Function Equals1(other As DemoClass) As Boolean Implements System.IEquatable(Of DemoClass).Equals
    If Me.number = other.number Then
      Return True
    Else
      Return False
    End If
  End Function
End Class

Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click
  Dim lst As New List(Of DemoClass)
  Dim dc1 As New DemoClass With {.amount = 123, .number = "123", .date = #1/2/2012#}
  Dim dc2 As New DemoClass With {.amount = 124, .number = "124", .date = #1/3/2012#}
  Dim dc3 As New DemoClass With {.amount = 123, .number = "123", .date = #1/2/2012#} 'same as dc1!!
  If Not lst.Contains(dc1) Then lst.Add(dc1)
  If Not lst.Contains(dc2) Then lst.Add(dc2)
  If Not lst.Contains(dc2) Then lst.Add(dc3) 'this won't get added!'
  MsgBox(lst.Count) 'should return 2'
End Sub

列表中的重复项目

3 个答案: