VBA - IF loop improvements - vba

Question

I'm currently running a macro which identifies duplicates in a workbook, however it identifies the first set off the index and doesn't tag the first set then which has led to me setting up a if statement to by pass this, which adds duplicate to the first instance too. This is taking a long time to do however and would like to improve this, if possible. Any suggestions would be greatly appreciated, I am new to VBA but have been learning bits as I've encountered new problems!
'Declaring the lastRow variable as Long to store the last row value in the Column1
Dim lastRow As Long
'matchFoundIndex is to store the match index values of the given value
Dim matchFoundIndex As Long
'iCntr is to loop through all the records in the column 1 using For loop
Dim iCntr As Long
Dim first_dup As Long
Dim tagging As Long
Dim item_code As String
'Finding the last row in the Column 1
lastRow = Range("B1000000").End(xlUp).Row
'
'looping through the column1
For iCntr = 2 To lastRow
'checking if the cell is having any item, skipping if it is blank.
If Cells(iCntr, 1) <> "" Then
'getting match index number for the value of the cell
matchFoundIndex = WorksheetFunction.Match(Cells(iCntr, 1), Range("A1:A" & lastRow), 0)
'if the match index is not equals to current row number, then it is a duplicate value
If iCntr <> matchFoundIndex Then
'Printing the label in the column B
Cells(iCntr, 4) = "Duplicate"
End If
End If
Next
For first_dup = 2 To lastRow
If Cells(first_dup, 5) = "Duplicate" Then
item_code = Cells(first_dup, 1)
For tagging = 2 To lastRow
If Cells(tagging, 1) = item_code Then
Cells(tagging, 5) = "Duplicate"
End If
Next
End If
Next
Example data:
item code
1
2
3
4
1 duplicate
2 duplicate
3 duplicate
4 duplicate
1 duplicate
2 duplicate
3 duplicate
4 duplicate

Answer 1

My first suggestion is not to over-complicate things, try using duplicate values conditional formatting to see if this helps:
Failing that, if you are desperate to find ONLY the duplicates, and not the first occurrence, you can use a formula like this: (In Cell B2 if your Data starts in A2, it will require a header row that doesn't match, or your first row will always match)
=IF(COUNTIF($A1:A$1,A2)>=1,"Duplicate","")
Which when pasted down your row of data could look something like this:
There are also VBA solutions if you are desperate for a VBA solution, but I thought I'd give you the simple ones first. Let me know how you get on in the comments.
Edit: you can just insert the above formula using VBA, with R1C1 notation, e.g.:
Sub test()
Range("B2:B" & Range("A1").End(xlDown).Row).FormulaR1C1 = "=IF(COUNTIF(R1C1:R[-1]C1,RC1)>=1,""Duplicate"","""")"
End Sub
I'll break this down so you know what is happening.
Range("B2:B" & Range("A1").End(xlDown).Row) selects the cells in column B between B2 and the last filled row in column A i.e. Range("A1").End(xlDown).Row (so this won't work if you expect blanks in column A as part of your data)
Then, it sets the R1C1 ref formula to "=IF(COUNTIF(R1C1:R[-1]C1,RC1)>=1,""Duplicate"","""")", where R1C1 means first row, first column, (i.e. $A$1)
R[-1]C1 means previous row, first column. For example,
If you are in B5, this would select A4.
If you are in A2, this would select A1.
If you are in A1, this would error out because you cant be in a row earlier than 1.
And RC1 means current row, first column.
Hope this helps!

Answer 2

The answer was the same as the initial code I presented, it's taking roughly 5 minutes for 30000 items so it isn't too bad at what it does.