LINQ grouping with custom comparer

Question

I'm trying to implement a linq grouping with a custom comparer. I have a datatable, I fill it with data, then I add the datarows to a
List(Of DataRow), then I select all the rows to a IEnumerable(Of Object()). After that, I would like to group the result with a custom comprarer.
This is the code:
Dim result As IEnumerable(Of Object())
Dim dt As New DataTable
Dim indexes As New List(Of Integer)
Dim groupedindexes As New List(Of Integer)
Dim datarows As New List(Of DataRow)
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
dt.Columns.Add("f1", Type.GetType("System.Char"))
dt.Columns.Add("f2", Type.GetType("System.Char"))
dt.Columns.Add("f3", Type.GetType("System.Char"))
For i = 0 To 100
dt.Rows.Add("a", "b", "c")
Next
indexes.Add(0)
indexes.Add(1)
indexes.Add(2)
groupedindexes.Add(0)
groupedindexes.Add(1)
groupedindexes.Add(2)
For i = 0 To dt.Rows.Count - 1
datarows.Add(dt.Rows(i))
Next
result = datarows.Select(Function(row) indexes.Select(Function(index) row(index)).ToArray)
Dim test = result.GroupBy(Function(row) groupedindexes.Select(Function(grpindex) row(grpindex)).ToArray, New compare)
End Sub
And this is the compare class:
Partial Class compare
Implements System.Collections.Generic.IEqualityComparer(Of Object())
Public Function Equals1(ByVal x() As Object, ByVal y() As Object) As Boolean Implements System.Collections.Generic.IEqualityComparer(Of Object()).Equals
Dim equal As Boolean = True
For i = 0 To x.Count - 1
If x(i) IsNot y(i) Then
equal = False
Exit For
End If
Next
Return equal
End Function
Public Function GetHashCode1(ByVal obj() As Object) As Integer Implements System.Collections.Generic.IEqualityComparer(Of Object()).GetHashCode
Dim hashcode As Integer
For i = 0 To obj.Count - 1
hashcode = hashcode + obj(i).GetHashCode
Next
Return hashcode
End Function
End Class
With the above code, I get all the 101 rows, but I would like to get only one row (a, b, c), since all the rows are the same. Therefore I wrote the custom comparer class. I'm new to this and I'm not sure, that I use it correct.
Can you advise me, how should I modify the code to get only one row?
Thanks.

Answer 1

Try code below.  I use a dictionary to group rows and then filter results to get unique rows.
Module Module1
Sub Main()
Dim dt As New DataTable
Dim dict As Dictionary(Of Integer, List(Of DataRow)) = dt.AsEnumerable() _
.GroupBy(Function(x) x.Field(Of Integer)("Col A"), Function(y) y) _
.ToDictionary(Function(x) x.Key, Function(y) compare(y.ToList()))
End Sub
Function compare(rows As List(Of DataRow)) As List(Of DataRow)
Dim results As New List(Of DataRow)
results.Add(rows.FirstOrDefault)
If (rows.Count > 1) Then
For i = 1 To (rows.Count - 1)
Dim unique As Boolean = True
Dim rowArray() As Object = rows(i).ItemArray
For j = 0 To (results.Count - 1)
Dim oldArray() As Object = results(j).ItemArray
For cols = 0 To (rowArray.Length - 1)
If rowArray(i) <> oldArray(j) Then
unique = False
Exit For
End If
Next cols
If unique = False Then
Exit For
End If
Next j
If unique = True Then
results.Add(rows(i))
End If
Next i
End If
Return results
End Function
End Module
jdweng