IF statement to ArrayFormula?

Question

我在D3中有一个公式，看起来像这样:

=IF(B3="","",B3-B2)

我如何填写整个列D(从D3)与该公式使用ArrayFormula?

Answer 1

=ARRAYFORMULA(IF(B3:B="",,B3:B-ARRAY_CONSTRAIN(B2:B,ROWS(B3:B),1)))

Answer 2

=ARRAYFORMULA(IF(B3:B501="","",B2:B500-B3:B501))