Group rows in sap script

[miske]

Hello everyone,
I have a custom SAP script used for displaying open Item list for customers. Its working fine but now I need to group all the rows that have the same Doc Number (value in RF140-BELEGNUM). In that grouped row dates would be the same, only Amount should be SUM-ed.

Here is a ss of the sap script MAIN window:

How can I do this? I know I should be doing something like this:

/: PERFORM group_rows IN PROGRAM <prog>

/: USING &INVAR1&

/: USING &INVAR2&

/: CHANGING &OUTVAR1&

/: CHANGING &OUTVAR2&

/: ENDPERFORM

Do I make some internal table where I group the rows? If so, how do I use that int. table in sap script?

BR to everyone.