Excel VBA compare values on multiple rows and execute additional code

I have the following task:
There are fields in my document, the combination of which needs to be compared, and if they are the same, another field on the same rows need to be updated.

So far, I add the values in arrays (skipping the first row as header, thus iNum = 2) with select statements per column and concatenate them per row for the comparison.

Dim conc As Range                               'Concatenated fields
Dim iconc() As Variant

ReDim iconc(UBound(iMatn) - 1, 1)

For iNum = 2 To UBound(iMatn)
                
    iconc(iNum - 1, 1) = iMatn(iNum, 1) & iVendr(iNum, 1) & iInd1(iNum, 1) & iInd2(iNum, 1)    'Current concatenation

    Select Case iNum - 1
    
    Case 2:                     'Compare two records
    
        If iconc(iNum - 2, 1) = iconc(iNum - 1, 1) Then         'Compare first and second records
            'Execute code to update the two fields from Extra field column
        End If

    Case 3:                     'Compare three records
    
        If AllSame(iconc(iNum - 3, 1), iconc(iNum - 2, 1), iconc(iNum - 1, 1)) Then
            'Execute code to update the three fields from Extra field column
        End If

I go through each value of the concatenation and compare if its the same as the previous ones with Case statement (I don't expect more than 4 or 5 to be the same, even though there could be a couple hundred of lines).
Thus I face two issues:

1. If there are 3 equal values, for example, the code first jumps to the case for 2. How can I make it so that it skips to the maximum value?
2. It needs to resume checking after the rows that were already checked. E.g. if the first two are the same, the code should start checking from the third one; basically to start at from the line after the last of any duplicate ones that are located.

Example

Image: the code needs to return that there are 3 equal rows (lines 2 to 4), update the respective cells on the "Extra field" column, proceed further (from line 5), return that there are 2 equal rows (lines 6 and 7), update the same as above again, proceed further (from line 8) etc.

Any help will be highly appreciated as I am stuck with this problem.

Thank you all.

To determine how many are in each group, in order to decide how you will update the extra fields column, I would use a Dictionary & Collection object.

eg:

'Set reference to Microsoft Scripting Runtime
'    (or use late-binding)

Option Explicit

Sub due()
  Dim myDict As Dictionary, col As Collection
  Dim i As Long, v As Variant
  Dim sKey As String
  Dim rTable As Range
  Dim vTable As Variant, vResults As Variant

'there are more robust methods of selecting the table range
'depending on your actual layout
'And code will also make a difference if the original range includes
'  or does not include the "Extra Field" Column
' Code below assumes it is NOT included in original data

Set rTable = ThisWorkbook.Worksheets("sheet2").Cells(1, 1).CurrentRegion

vTable = rTable

Set myDict = New Dictionary
For i = 2 To UBound(vTable)
    sKey = vTable(i, 1) & vTable(i, 2) & vTable(i, 3) & vTable(i, 4)
    Set col = New Collection
    If Not myDict.Exists(sKey) Then
        col.Add Item:=WorksheetFunction.Index(vTable, i, 0)
        myDict.Add Key:=sKey, Item:=col
    Else
        myDict(sKey).Add Item:=WorksheetFunction.Index(vTable, i, 0)
    End If
Next i

For Each v In myDict.Keys
    Select Case myDict(v).Count
        Case 2
            Debug.Print v, "Do update for two rows"
        Case 3
            Debug.Print v, "Do update for three rows"
        Case Else
            Debug.Print v, "No update needed"
    End Select
Next v

End Sub

=>

1234V22341212 Do update for three rows
1234v22351215 No update needed
2234v22361515 Do update for two rows
2234v22361311 No update needed

Although, I would probably use Power Query (available in Windows Excel 2010+ and 365) which can easily group by the four columns and return a count. You can then add a new column depending on that count.

Not knowing the nature of your updating Extra Field and the difference between what happens for 2, 3, 4, ... the same, it is not possible to supply any code for that purpose.

In general, you would

• expand the array for each dictionary item
• Add the extra column if it's not already there
• Do the update
• Add that to a pre-dimensioned results array
• Write the results array back to the worksheet

Note that this method of working with VBA arrays will execute an order of magnitude faster than doing repeated worksheet accessing, but the code is longer.

If you use a look ahead to the next row (rather than look behind) you can determine the end of the group and process accordingly.

Option Explicit

Sub CompareRows()

    Dim ws As Worksheet, ar, arExtra
    Dim lastrow As Long, n As Long, i As Long, k As Long
    Dim s As String, sNext As String, rng As Range, iColor As Long
    
    Set ws = ThisWorkbook.Sheets("Sheet1")
    With ws
        lastrow = .Cells(.Rows.Count, "A").End(xlUp).Row
        ar = .Range("A1:D1").Resize(lastrow)
        n = 1
        For i = 1 To UBound(ar)
        
            ' look ahead to next line
            If i = UBound(ar) Then
                sNext = ""
            Else
                sNext = ar(i + 1, 1) & "_" & ar(i + 1, 2) & _
                "_" & ar(i + 1, 3) & "_" & ar(i + 1, 4)
            End If
               
            If i > 1 Then ' skip header
                ' increment count if matched
                If sNext = s Then
                     n = n + 1
                
                ' process group using counter n
                Else
                    If n >= 2 Then
                        ' first row of group
                        Set rng = .Cells(i, "E").Offset(1 - n)
                           
                        If n >= 3 Then
                            iColor = rgb(128, 255, 128) ' green
                        Else
                            iColor = rgb(255, 255, 128) ' yellow
                        End If
                            
                        'code to update n rows in Extra column
                        rng.Resize(n).Value = n
                        rng.Offset(, -4).Resize(n, 5).Interior.color = iColor
                        
                        k = k + 1 ' group count
                    End If
                    n = 1
                End If
            End If
            s = sNext
        Next
    End With
    MsgBox k & " groups found", vbInformation

End Sub


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