Creating an IEqualityComparer for Arrays and Distinct

Question

I have an array of arrays of integer (a jagged array, Integer()()) from which I want to remove duplicates. For example, if I have the following:

Dim testvalues As Integer()() = {
    ({2, 4, 3, 1, 5}),
    ({1, 3, 5, 2, 4}),
    ({5, 4, 3, 2, 1}),
    ({1, 2, 3, 4, 5}),
    ({2, 4, 1, 3, 5}),
    ({1, 2, 3, 4, 5}),
    ({5, 4, 3, 2, 1}),
    ({1, 2, 3, 4, 5})}

I want to use the Distinct() method to get the following:

Dim distincttestvalues As Integer()() = {
    ({2, 4, 3, 1, 5}),
    ({1, 3, 5, 2, 4}),
    ({5, 4, 3, 2, 1}),
    ({1, 2, 3, 4, 5}),
    ({2, 4, 1, 3, 5})}

I have been unable to find an existing way to do this, so I figured the best solution would be to create an IEqualityComparer (which I have never done before) that uses the SequenceEqual method. Is this the best way to remove duplicate arrays, or do I need to resort to manually finding them using loops & if statements? Thanks.

Answer 1

I think I managed to find an answer that I like, I created the following class by inheriting from EqualityComparer:

Public Class ArrayComparer(Of T) : Inherits EqualityComparer(Of T())
    Public Overrides Function Equals(x As T(), y As T()) As Boolean
        Return x.SequenceEqual(y)
    End Function
    Public Overrides Function GetHashCode(obj As T()) As Integer
        Return obj.Length.GetHashCode()
    End Function
End Class

And then I just used .Distinct(New ArrayComparer(Of Integer)()) in my code. I knew there had to be a simple way to do it, I think this was just one of those first time things (and I have always been somewhat confused by the GetHashCode method). But this seems to work well enough (at least for my scenario).

Answer 2

Hello,

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Thanks.

Answer 3

Hi, you can write your own Extension like in this console demo:

Imports System.Runtime.CompilerServices

Module Module48

  Sub Main()
    Try
      Call (New Demo).Execute()
    Catch ex As Exception
      Console.WriteLine(ex.ToString)
    End Try
    Console.WriteLine("Continue enter key")
    Console.ReadKey()
  End Sub

  Friend Class Demo
    Friend Sub Execute()
      Dim testvalues As Integer()() = {
        ({2, 4, 3, 1, 5}),
        ({1, 3, 5, 2, 4}),
        ({5, 4, 3, 2, 1}),
        ({1, 2, 3, 4, 5}),
        ({2, 4, 1, 3, 5}),
        ({1, 2, 3, 4, 5}),
        ({5, 4, 3, 2, 1}),
        ({1, 2, 3, 4, 5})}

      Dim distincttestvalues = testvalues.DistinctTest

      For i = 0 To distincttestvalues.GetUpperBound(0)
        For k = 0 To distincttestvalues(i).GetUpperBound(0)
          Console.Write($" {distincttestvalues(i)(k)}")
        Next
        Console.WriteLine()
      Next

    End Sub
  End Class

End Module

Public Module ArrayExtensions

  <Extension()>
  Public Function DistinctTest(inp As Integer()()) As Integer()()
    Dim cacheList As New List(Of Integer())
    For i = 0 To inp.GetUpperBound(0)
      Dim sw As Boolean = False
      For k = 0 To cacheList.Count - 1
        If inp(i).SequenceEqual(cacheList(k)) Then
          sw = True
          Exit For
        End If
      Next
      If Not sw Then cacheList.Add(inp(i))
    Next
    Dim out(cacheList.Count - 1)() As Integer
    For i = 0 To out.GetUpperBound(0)
      out(i) = cacheList(i)
    Next
    Return out
  End Function

End Module