Calculate column based on previous value of itself in previous row

[rtrigor]

Hello, I have this initial table:

TableA:

Row	ValueA	PCT
1	100.000	0
2	100.000	8%
3	100.000	5%
4	100.000	7%
5	100.000	6%
6	100.000	3%
7	100.000	5%

And I need to perform the following calculation for ValueB from ValueC:

Row	ValueA	PCT	ValueB: WHEN Row=1, ValueA WHEN Row>1, (Pevious(ValueB) - Previous(ValueC))	ValueC = ValueB x PCT
1	100.000	0	100.000	-
2	100.000	8%	100.000	8.000,00
3	100.000	5%	92.000	4.600,00
4	100.000	7%	87.400	6.118,00
5	100.000	6%	81.282	4.876,92
6	100.000	3%	76.405	2.292,15
7	100.000	5%	74.113	3.705,65

Any clues?

I couldn't find a formula that worked using Previous() neither Peek().

[West69]

I have a similar need for a vectorized solution. It would be nice if pandas provided version of apply() where the user's function is able to access one or more values from the previous row as part of its calculation or at least return a value that is then passed 'to itself' on the next iteration. Wouldn't this allow some efficiency gains compared to a for loop?

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