ArrayFormula to calculate stock position by date

I am creating a stock transaction tracking sheet where i enter buys and sells etc. I have a formula that can calculate a running position total but I cannot figure out how to convert it to an array formula.

The formula I have so far is

SUM(INDEX(FILTER(A:D, B:B=B2, row(B:B) <= row(B2)),,4))

Here's a copy of the sheet