Does anyone have some wizzy code or bright ideas?

Question

I have a string variable - varchar2(240) maximum - which is arbitarily filled with 3 letter codes. Any one or more of these codes may be duplicated within the string. What I need to do is to strip out all the duplications and end up with a single contiguous string containing all the unique code options. e.g.
Initial string 'AAABBBCCCBBBDDDAAAEEEBBB'
should end up as :-
'AAABBBCCCDDDEEE'
Hope this makes sense - also there is no need to place the unique codes in any kind of order.
Thanks for your help...

Answer 1

And in 10g, regular expressions and MODEL clause can do the job:
WITH t AS (SELECT 'AAABBBCCCBBBDDDAAAEEEBBB' col1
             FROM dual
SELECT c1
     , c2
  FROM t
  MODEL
   DIMENSION BY (0 dim)
   MEASURES(col1 c1, CAST ('' AS VARCHAR2(255)) c2, CAST ('x' AS VARCHAR2(255)) c3)
   RULES ITERATE(99) UNTIL (c3[0] IS NULL)
   (c3[0] = REGEXP_SUBSTR(c1[0], '([A-Z])\1{2}', 1, ITERATION_NUMBER+1)
   ,c2[0] = c2[0] || CASE WHEN NVL(INSTR(c2[0], c3[0]), 0) = 0 THEN c3[0] END
C1                             C2
AAABBBCCCBBBDDDAAAEEEBBB       AAABBBCCCDDDEEE      C.