I'm doing an addon the modifies the account views to better cope with our accountant's habits and ergonomics. She has asked to replace the amount_currency column with a pair of currency debit and currency credit. We have done so with a couple of functional fields that modify the amount_currency accordingly.

But now she asks for the totals of those new columns. This sum only makes sense when grouping by currency (a filter we have added). So, how could I show the total only when grouping by currency?