This requires COUNTIFS (or SUMIFS with a logical trick). Assume Column A is Category, Column B is Item. In C2:
=IF(ISBLANK(A2),"",COUNTA(A$2:A2))
This mimics the behavior of a for loop in programming without VBA. The formula carries its own history. It is stateful —each cell’s output depends on the count of previous cells. This is the foundation of running totals and ranked lists. However, it fails catastrophically with filters or hidden rows, because COUNTA sees hidden cells. 2. The Invisible Condition: Numbering Filtered Data When you apply a filter to a table, rows become hidden. A standard COUNTA formula will break the sequence, creating gaps (e.g., 1, 2, 5, 7). The user needs a numbering system that sees only the visible universe. numerar celdas en excel con condiciones
The solution lies in a counter-intuitive use of COUNTIF or COUNTA with a mixed reference. In cell B2, you enter: This requires COUNTIFS (or SUMIFS with a logical trick)