Nested loop conditional

Question

Supposed I have this table:

 TDID    TDLINE
 F04     04-AA
 F04     04-BB    <-- call a function
 F05     05-AA
 F05     05-BB    <-- call a function
 F06     06-AA    <-- call a function

I would like to call a function while the TDID field is not the same as the previous one. I have the code below, it works but somehow it's not perfectly works (it missed the last row):

LOOP AT lines ASSIGNING <fs1>.
  IF <fs2> IS INITIAL.
    <fs2> = <fs1>.
  ELSE.
    li_line-tdline = <fs2>-tdline.
    APPEND li_line.

    IF <fs1>-tdid NE <fs2>-tdid.
      li_thead-tdid = <fs2>-tdid.

      CALL FUNCTION 'SAVE_TEXT'
        EXPORTING
          header          = li_thead
          savemode_direct = 'X'
        TABLES
          lines           = li_line

      CLEAR: li_thead,
             li_line.
      FREE:  li_thead,
             li_line.
    ENDIF.
  ENDIF.
ENDLOOP.

---

ANSWER

Thank you to vwegert for the answer:

LOOP AT lines ASSIGNING <fs1>.
  AT NEW tdid.
    REFRESH li_thead.
    REFRESH li_line.

    li_thead-tdid     = <fs1>-tdid.
    APPEND li_thead.
  ENDAT.

  li_line-tdline    = <fs1>-tdline.
  APPEND li_line.

  AT END OF tdid.
    CALL FUNCTION 'SAVE_TEXT'
      EXPORTING
        header          = li_thead
        savemode_direct = 'X'
      TABLES
        lines           = li_line
  ENDAT.
ENDLOOP.

Answer 1

Assuming that the table is sorted by TDID and no field left of TDID changes more frequently than TDID:

LOOP AT lines ASSIGNING <fs1>.
  AT NEW tdid.
    REFRESH some_other_tab.
  ENDAT.
  APPEND <fs1> TO some_other_tab.
  AT END OF tdid.
    CALL FUNCTION ...
  ENDAT.
ENDLOOP.

Answer 2

The unpredictability as mentioned by vwegert comes because the characters fields next to the field on which Control statement is applied are converted to asterisks(*). If you want to use these values in the control statement make sure you copy the values in a temporary table and loop on it instead of the original internal table and use the values using READ on the original internal table. Also keep in mind that control statement considers all columns to the left of the column being used in the statement for it's condition.