FORM drittmeiste_geburtstage CHANGING ct_data TYPE tt_data.

  DATA: lt_counters TYPE TABLE OF i,
        t_ergebnis  LIKE ct_data.

  LOOP AT ct_data ASSIGNING FIELD-SYMBOL(<line>) GROUP BY ( birthday = <line>-birthday size = GROUP SIZE ) ASCENDING WITHOUT MEMBERS REFERENCE INTO DATA(grp).
    APPEND grp->size TO lt_counters.
  ENDLOOP.

  SORT lt_counters DESCENDING.

  DATA(lv_count) = VALUE i( lt_counters[ 3 ] OPTIONAL ). "CHECK lv_count IS NOT INITIAL.
  WRITE:/ 'Drittmeist:', lv_count.

  LOOP AT ct_data ASSIGNING FIELD-SYMBOL(<line2>) GROUP BY ( birthday = <line2>-birthday size = GROUP SIZE ) ASCENDING REFERENCE INTO DATA(grp2).
    IF grp2->size = lv_count.
      LOOP AT GROUP grp2 ASSIGNING FIELD-SYMBOL(<erg>).
        APPEND <erg> TO t_ergebnis.
      ENDLOOP.
    ENDIF.
  ENDLOOP.

  ct_data = t_ergebnis.
ENDFORM.