Regexp Challenge

572471 · May 11, 2007 10:18AM

Hello, everyone.

I think it's impossible, but still maybe there would be some thoughts.
Well, the question is:
I have a sentence.
Is it possible to replace particular words with the others?
E.g. sentence 'I want milk'
What I want is: to replace 'I' with 'He',
'want' with 'wants' and 'milk' with 'sugar'.

The main idea is to use only one level of nesting in "replace" function.
I have an example, the first column is some kinda "prototype". It has the logic which I want to implement, but it's not working properly.
The two other columns are working variants, but they are not what I want.

SQL> with t as (select 'I want milk' str from dual)
  2  --
  3  select regexp_replace(str, '(I|want|milk)', decode('\1', 'I', 'He', 'want', 'wants', 'milk', 'sugar', '\1')) smth_like_this,
  4         replace(replace(replace(str,'I', 'He'),'want', 'wants'), 'milk', 'sugar') what_is_needed,
  5         (select str from dual
  6          model
  7           reference r
  8            on  (select 1 rn, 'I' from_str, 'He' to_str from dual union all
  9                select 2, 'want', 'wants' from dual union all
 10                select 3, 'milk', 'sugar' from dual)
 11            dimension by (rn)
 12            measures (from_str f, to_str t)
 13            main m
 14             dimension by (0 dim)
 15             measures (cast(str AS VARCHAR2(4000)) str)
 16             rules iterate (1000) until (presentv(f[iteration_number+1],1,0)=0)
 17              (str[0] = replace(str[0], r.f[iteration_number+1], r.t[iteration_number+1]))
 18           ) from t
 19  /

SMTH_LIKE_THIS WHAT_IS_NEEDED (SELECTSTRFROMDUALMODELREFEREN
-------------- -------------- --------------------------------------------------------------------------------
I want milk    He wants sugar He wants sugar

cd_2 · May 11, 2007 2:47PM

I don't see a pure regex solution since there is no appropriate loop construct, this is what I came up with:

WITH t AS (SELECT 'I want milk' col1
             FROM dual)
   , u AS (SELECT 'I' orig, 'He' repl
             FROM dual
            UNION 
           SELECT 'want', 'wants'
             FROM dual
            UNION
           SELECT 'milk', 'sugar'
             FROM dual
          )   
SELECT MAX(SYS_CONNECT_BY_PATH(NVL(u.repl, t.word), ' '))
  FROM (SELECT REGEXP_SUBSTR(t.col1, '[^ ]+', 1, LEVEL) word 
             , level lvl
          FROM t
          CONNECT BY LEVEL <= LENGTH(REGEXP_REPLACE(t.col1, '([^ ]+) *', '1'))
       ) t
     , u
 WHERE t.word(+) = u.orig    
 START WITH t.lvl = 1
 CONNECT BY PRIOR t.lvl = t.lvl - 1
  ;

C.

John Spencer · May 11, 2007 3:21PM

What I find interesting is that the DECODE seems to recognize the back reference in the else bit, but not as in expression bit.

This leaves the string unchanged:

SQL> SELECT REGEXP_REPLACE(str, '(I|want|milk)',

  2                        DECODE('\1', 'I', 'He',

  3                                     'want', 'wants',

  4                                     'milk', 'sugar', '\1')) smth_like_this

  5  FROM (SELECT 'I want milk please' str FROM dual);


SMTH_LIKE_THIS

------------------

I want milk please

But if we replace the back reference in the else part with fixed text, we get:

SQL> SELECT REGEXP_REPLACE(str, '(I|want|milk)',

                      DECODE('\1', 'I', 'He',

                                   'want', 'wants',

                                   'milk', 'sugar', 'fred')) smth_like_this

FROM (SELECT 'I want milk please' str FROM dual);  2    3    4    5


SMTH_LIKE_THIS

---------------------

fred fred fred please

John

cd_2 · May 11, 2007 3:55PM

I don't think that DECODE recognizes the backreference, all it does is select the ELSE part of it's statement since there is no match with the literal '\1'. You'll get the same result with this:

SELECT REGEXP_REPLACE(str, '(I|want|milk)', 'fred')
  FROM (SELECT 'I want milk please' str 
          FROM dual);

C.

572471 · May 11, 2007 4:11PM

2 John Spencer

What I find interesting is that the DECODE seems to
recognize the back reference in the else bit, but not
as in expression bit.

Fully agree with cd
decode takes '\1' as just a string '\1' but not a back reference.
I used it just trying to illustrate what I wanted.

2 cd
You made a smal mistake: (+) in the wrong place.
But the idea is clear. Thanks.

SQL> WITH t AS (SELECT 'I want please milk' col1
  2               FROM dual)
  3     , u AS (SELECT 'I' orig, 'He' repl
  4               FROM dual
  5              UNION
  6             SELECT 'want', 'wants'
  7               FROM dual
  8              UNION
  9             SELECT 'milk', 'sugar'
 10               FROM dual
 11            )
 12  SELECT MAX(SYS_CONNECT_BY_PATH(NVL(u.repl, t.word), ' '))
 13    FROM (SELECT REGEXP_SUBSTR(t.col1, '[^ ]+', 1, LEVEL) word
 14               , level lvl
 15            FROM t
 16            CONNECT BY LEVEL <= LENGTH(REGEXP_REPLACE(t.col1, '([^ ]+) *', '1'))
 17         ) t
 18       , u
 19   WHERE t.word = u.orig<strong>(+)</strong>
 20   START WITH t.lvl = 1
 21   CONNECT BY PRIOR t.lvl = t.lvl - 1
 22  /

MAX(SYS_CONNECT_BY_PATH(NVL(U.
--------------------------------------------------------------------------------
 He wants please sugar

SQL>

well, it's a pity there's no such a functionality.

572471 · May 11, 2007 4:41PM

cd
if you have more than one string in table t
you should change the query that way:

SQL> WITH t AS (SELECT 'I want please milk' col1

  2               FROM dual union all

  3             select 'He wants milk' from dual)

  4     , u AS (SELECT 'I' orig, 'He' repl

  5               FROM dual

  6              UNION

  7             SELECT 'want', 'wants'

  8               FROM dual

  9              UNION

 10             SELECT 'milk', 'sugar'

 11               FROM dual

 12            )

 13           --

 14  SELECT max(SYS_CONNECT_BY_PATH(NVL(u.repl, t.word), ' '))

 15    FROM (SELECT rn, REGEXP_SUBSTR(t.col1, '[^ ]+', 1, LEVEL) word

 16               , level lvl

 17            FROM (select rownum rn, t.* from t)t

 18            CONNECT BY LEVEL <= LENGTH(REGEXP_REPLACE(t.col1, '([^ ]+) *', '1'))

 19             and prior rn = rn

 20             and prior dbms_random.value is not null

 21         ) t

 22       , u

 23   WHERE t.word = u.orig(+)

 24   START WITH t.lvl = 1

 25   CONNECT BY PRIOR t.lvl = t.lvl - 1

 26     and prior rn = rn

 27     group by rn

 28  /


MAX(SYS_CONNECT_BY_PATH(NVL(U.

--------------------------------------------------------------------------------

 He wants please sugar

 He wants sugar

but you can see a small drawback.
in the second sentence word "wants" hasn't change although it includes word "want".
I think model is better here:

SQL> WITH t AS (SELECT 'I want please milk' col

  2               FROM dual union all

  3             select 'He wants milk' from dual)

  4     , u AS (SELECT 'I' orig, 'He' repl

  5               FROM dual

  6              UNION

  7             SELECT 'want', 'wants'

  8               FROM dual

  9              UNION

 10             SELECT 'milk', 'sugar'

 11               FROM dual

 12            )

 13           --

 14  select col from (select rownum rn, t.* from t)

 15   model

 16    reference r

 17     on (select * from (select rownum rn, u.* from u))

 18      dimension by (rn)

 19      measures(orig, repl)

 20    main m

 21     dimension by (rn)

 22     measures(cast(col as varchar2(4000)) col)

 23      rules iterate (1000) until (presentv(orig[iteration_number+1],1,0)=0)

 24       (col[ANY] = replace(col[CV()], r.orig[iteration_number+1], r.repl[iteration_number+1]))

 25  /


COL

--------------------------------------------------------------------------------

He wants please sugar

He wantss sugar

John Spencer · May 11, 2007 5:09PM

cd:

While I acknowledge your rexexp expertise, the DECODE clearly does recognize the back reference, at least in part. I agree that it is comparing the literal string \1 with I and want and milk. Certainly the literal string \1 does not match any of those strings, so the else part is evaluated. The \1 in the else part appears to evaluate to the back reference. If it was again being interpreted as a literal string, I would expect to get the result:

\1 \1 \1 please

instead of getting the original string back.

John

572471 · May 11, 2007 5:27PM

If it was again being interpreted as a
literal string, I would expect to get the result:

\1 \1 \1 please

yep, sounds reasonable.
really strange behaviour.
So, somehow it recognizes backreferences, but only partially in the else part of decode or case.

SQL> SELECT REGEXP_REPLACE(str, '(I|want|milk)', case '\1' when 'I' then 'He' else '\1' end),
  2         REGEXP_REPLACE(str, '(I|want|milk)', case '\1' when '\1' then 'He' else '\1' end)
  3    FROM (SELECT 'I want milk please' str
  4            FROM dual);

REGEXP_REPLACE(STR,'(I|WANT|MI    REGEXP_REPLACE(STR,'(I|WANT|MI
--------------------------------- ------------------------------------
I want milk please                He He He please

SQL>

cd_2 · May 11, 2007 10:06PM

In which case? In your first example, the result string of the decode should be '\1' and regexp can use that literal to return the backreference. All DECODE does is prepare a literal that can be used as result pattern.

C.

MichaelS · May 12, 2007 11:48AM

XML is able to do this as well: ;-)

michaels>  with t as (
 select 'I want please milk' col from dual union all
 select 'He wants milk' from dual
), 
u as (
 select 'I' orig, 'He' repl from dual union  
 select 'want', 'wants'     from dual union 
 select 'milk', 'sugar'     from dual 
)
select col, 
       value(t) repl
  from t,
       xmltable('declare function local:replace_all($str, $orig, $repl)
                 {
                   if($orig[1]) then 
                     local:replace_all(ora:replace($str, $orig[1], $repl[1]), subsequence($orig, 2), subsequence($repl, 2))
                   else ($str)
                 };
                     
                 local:replace_all(/col, $u/ROWSET//ORIG//text(), $u/ROWSET//REPL//text())
                 ' passing xmltype('<col>'  || col  || '</col>'),
                           xmltype(cursor(select * from u)) as "u") t

COL                REPL                     
------------------ -------------------------
I want please milk He wants please sugar    
He wants milk      He wantss sugar          


2 rows selected.

572471 · May 12, 2007 12:40PM

thanks, michaels.

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