Auto-increment where cell values not NULL

Question

I have a list of items purchased, like below.

A   |  B      |  C    |  D           |  E         |

id  |  item   |  qty  |  unit price  |  subtotal  |

I'd like to have the column id to automatically increment correctly in each row where the subtotal is not null. How can I do it?

Answer 1

=ARRAYFORMULA(IF(LEN(B2:B), SUBSTITUTE(COUNTIFS(IF((LEN(E2:E)) * (E2:E>0), 1, ),
 IF((LEN(E2:E)) * (E2:E>0), 1, ), ROW(B2:B), "<="&ROW(B2:B)), 0, ), ))