Help needed on Group by Expression for complex RTF template design

Hi All,

We have a requirement where in we need to group Transaction lines (for Invoice RTF Template) based on a column Flag (y/n) , but the problem is flag is not tied at a header or transactionID level. It is available only for each Transaction lines for a particular Transaction Number/Invoice number. Example is as shown below.

Transaction #123:

Transaction Lines:

1 Y

2 Y

3 Y

Transaction #345:

Transaction Lines:

1 N

2 N

So for Transaction #123, it should be grouped and for Transaction #345 RTF template should render individual lines.

Any suggestions/ideas would be helpful