vba get rows number in each group in excel

Hello,

This can be done without VBA, just with a formula. In the Calculate column try

=IF(A2<>A1,COUNTIF(A:A,A2),"")

starting in row 2 and copy down.

This assumes that the data is sorted by the ID column and that there are no blank rows in the data. See attached sample file.

cheers, teylyn
BlockRows.xlsx

Thanks, this works very well. I have another question:

Here is my excel, the first column is order ID, the second column Qty is kind of group on ID column, how can I get sum  of each group and write to the calculate column ( only the first row of each group) ? Thanks,

ID     Qty    calculate

1       1          1

2       3         5

2       2      

5      1          6

5      3      

5      1

5      1

Try this formula for second question:
=IF(MATCH(A2,A:A,0)=ROW(),SUMIF(A:A,A2,B:B),"")

If you actually did want VBA instead of teylyn's excellent suggestion which I would also recommend, here is an update of the file with sample code

Sub CountID()
For Each c In Range("A2:A" & ActiveCell.SpecialCells(xlCellTypeLastCell).Row)
  i = i + 1
  j = j + 1
  If c.Value <> c.Offset(1, 0).Value Then
    Range("A2").Offset(j - i, 2).Value = i
    i = 0
  End If
Next c
End Sub

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BlockRows.xlsm