Google spreadsheet relative row numbering + skip empty cell - excel

Question

Using Google spreadsheet, I need a column to show relative row numbering, so that:
Spreadsheet rows can be moved around, and numbering stays relative (meaning that if I move row number 12 between rows 4 and 5, this row becomes number 5, previous 5 becomes 6, etc.)
Using a condition based upon a cell value in a given row, the row numbering cell may be empty (or not); if empty, that row number is being skipped, and numbering takes back up in the next row where the condition is unmatched.
Here is an example:
| Row nbr | B col. | [Explanation] |
|---------|:-------:|-------------------------------------|
| R01 | Value 1 | |
| R02 | Value 1 | |
| R03 | Value 2 | |
| | Value 3 | Col. B value = 3 => Col. A is empty |
| R04 | Value 2 | Numbering takes up |
| R05 | Value 1 | |
| | Value 3 | Col. B value = 3 => Col. A is empty |
| R06 | Value 2 | Numbering takes up |
| ETC. | | |
Here, the condition (to skip numbering) would be "IF corresponding B cell = Value 3" (then skip numbering)
Right now, I'm using a formula that matches requirement #1 above:
=ROW(INDIRECT("A"&ROW()&":A"))-9
(The trailing "-9" is just an offset so numbering can start at 01 from row 10).
So basically, I need to adapt (or change) this code so that besides relative numbering, for row N, if corresponding B column cell value = XYZ, then A column cell is empty (vs. numbered): that row is being skipped, and numbering takes back up from N on the next row where the B cell value ≠ XYZ.
Here's a Google spreadsheet example.
Many TIA's.

Answer 1

I strongly recommend not to use ROW() with explicitly specified offset in formula because should you delete/add rows above your table, your will have to adjust formulas in all cells. Here's my solution (column A:A is row numbers, B:B - values, start adding formula in cell A10):
=IF($B10="Value 3","",ROWS($B$10:$B10)-COUNTIF($B$10:$B10,"Value 3"))
Or if you insist on relative rows (change 10 to your offset from top):
=IF(INDIRECT("B"&ROW())="Value 3","",ROWS(INDIRECT("B"&10&":B"&ROW()))-COUNTIF(INDIRECT("B"&10&":B"&ROW()),"Value 3"))