ITAB - look for duplicates

Question

I want to do something like this....
Let's say my ITAB has MATNR & DUP fields & let's say ITAB has entries like this...
ITAB-MATNR      ITAB-DUP
123
123
345
456
if any of the MATNR's are repeated in ITAB I want to flag DUP for such repeated records so the ITAB would look like below......
ITAB-MATNR      ITAB-DUP
123
123                    X
345
456
Please note : only the records repeated after the first unique record should be flagged.

Answer 1

Try this
REPORT  zrich_0001.
TYPE-POOLS: abap.
TYPES: BEGIN OF ttab,
        matnr(18) TYPE c,
        dup TYPE abap_bool,
       END OF ttab.
DATA: itab TYPE TABLE OF ttab.
DATA: wa LIKE LINE OF itab.
DATA: itab_copy TYPE TABLE OF ttab.
DATA: wa_copy LIKE LINE OF itab_copy.
DATA: tabix TYPE i.
wa-matnr = '000000000000000123'.  APPEND wa TO itab.
wa-matnr = '000000000000000123'.  APPEND wa TO itab.
wa-matnr = '000000000000000123'.  APPEND wa TO itab.
wa-matnr = '000000000000000345'.  APPEND wa TO itab.
wa-matnr = '000000000000000456'.  APPEND wa TO itab.
wa-matnr = '000000000000000456'.  APPEND wa TO itab.
itab_copy = itab.
LOOP AT itab_copy INTO wa_copy.
  tabix = sy-tabix + 1.
  LOOP AT itab INTO wa FROM tabix
             WHERE matnr = wa_copy-matnr.
    wa-dup = abap_true.
    MODIFY itab FROM wa.
  ENDLOOP.
ENDLOOP.
LOOP AT itab INTO wa.
  WRITE:/ wa-matnr, wa-dup.
ENDLOOP.
Regards,
Rich Heilman