Position size in order book

Hi, I am debugging a strategy by going through my order book, but missing
the net position of my strategy in the output:

ob <- getOrderBook("xyz")$xyz$ABC
ob.df <- data.frame(Date=time(ob),coredata(ob))

View(ob.df)


Is there a way to display the actual position size line by line with each
trade in ob.df?

Many thanks in advance,
Peter