def _swap_fields(self, panes, switch_func):
        seen = set()
        for pane in panes:
            entries = self.loader.accounts.entries_for_account(pane.account)
            txns = dedupe(e.transaction for e in entries)
            for txn in txns:
                if txn.affected_accounts() & seen:
                    # We've already swapped this txn in a previous pane.
                    continue
                switch_func(txn)
            seen.add(pane.account)
        self.import_table.refresh()