Extract, Replace, Extract/Replace Only Particular?

[Cliff Nichols]

I find myself in a situation that before I go ahead and "Just Do It" myself, are there functions that Extract, or Replace only certain occurrences of a matching string?

Reason I ask is say for simplicity, In this example I will say Replace (I will worry about Extract etc later, I just need to know if what I am about to write is reinventing the wheel or not)

Example: "blackcat, white cat ,blue cat, what is a cat?, yadda yadda"
Command to execute: Remove second occurrence of the word "cat"
Resulting string: "blackcat, white < The word CAT deleted from here >,blue cat, what is a cat?, yadda yadda"

I know it can easily be done, but just wondered if its already done? or worthwhile writing a wrapper for?

[John Strasser]

Yes, there are functions Remove, Replace, and extract (in addition to the classic MID$, etc).

In fact there's a whole passel of functions that you can use. Probably you'll have to INSTR to find the specific occurrance you're looking for, but then replace or remove will do the job.

[John Gleason]

Yeah, I'd do some more testing, but here's an idea:

#COMPILE EXE
#DIM ALL
         'qReplace optimistically stands for quickReplace. Umm, okay.
FUNCTION qReplace(origS AS STRING, fs AS STRING, cnt AS LONG, rs AS STRING) AS STRING
   LOCAL pos1, pos2, tCnt AS LONG
   pos2 = 1

   DO
      pos1 = INSTR(pos2, origS, fs)
      IF pos1 > 0 THEN         'is there a match?
         INCR tCnt             'is it the match # we want?
         IF tCnt = cnt THEN
            FUNCTION = LEFT$(origS, pos1 - 1) & rs & MID$(origS, pos1 + LEN(fs))
            EXIT FUNCTION
         END IF
      END IF
      pos2 = pos1 + 1
      IF pos1 = 0 THEN         'no match or went beyond str len
         FUNCTION = origS
         EXIT FUNCTION
      END IF
   LOOP

END FUNCTION

FUNCTION PBMAIN () AS LONG
    LOCAL xs AS STRING, ii AS LONG

    xs = "blackcat, white cat ,blue cat, what is a cat?,ackcat, white cat ,blue cat, what is a cat?, yadda yadda"

    FOR ii = 1 TO 11
       ? qReplace(xs, "cat", ii, "")       'replace with ""
       ? qReplace(xs, "cat", ii, "dog")    'replace with "dog"
    NEXT

END FUNCTION

[Chris Holbrook]

oops!

[John Gleason]

I noticed you can make the function above into a single IF-THEN-ELSE. Also you may want to return an empty string on no match rather than a copy.

   DO
      pos1 = INSTR(pos2, origS, fs)
      IF pos1 > 0 THEN
         INCR tCnt
         IF tCnt = cnt THEN
            FUNCTION = LEFT$(origS, pos1 - 1) & rs & MID$(origS, pos1 + LEN(fs))
            EXIT FUNCTION
         END IF
      ELSE
         FUNCTION = origS    'You could also say FUNCTION = "" and get an empty string if there is no match.
         EXIT FUNCTION
      END IF
      pos2 = pos1 + 1
   LOOP

[Michael Mattias]

Well, you can surely write this easily enough as shown above. (or with regular expressions).

But if you really think it's a valuable suggestion, why don't you send in a new feature suggestion asking for an enhancement to INSTR?

 iPos = INSTR ([startpos&], lookin, lookfor [,OCCUR occurNo&])

Something like that, anyway. With the already optional first parameter, the syntax might get a little clumsy. Especially considering that if my own NFS for adding a case-insensitive option to INSTR is implemented there might be an even bigger fight for space in the parameter string.

???

iPos = INSTR ([startpos&], lookin, lookfor [,OCCUR occurNo&] [,UCASE])

????

[Charles Dietz]

I couldn't help but want to take a swing at this pitch...

FUNCTION fInstr(start AS LONG, s AS STRING, t AS STRING, nOccur AS LONG, repl AS STRING) AS STRING
   LOCAL i, m, mm AS LONG
   mm = MAX(start, 1)
   FOR i = 1 TO nOccur
      m = INSTR(mm, s, t): mm = m + LEN(t)
   NEXT i
   FUNCTION = LEFT$(s, m - 1) + repl + MID$(s, mm)
END FUNCTION

FUNCTION PBMAIN
   LOCAL s, ss, t AS STRING
   LOCAL m, mm, n, i AS LONG
   s = "blackcat, white cat ,blue cat, what is a cat?, yadda yadda"
   MSGBOX fInstr(0, s, "cat", 2, "dog") 
END FUNCTION

[John Gleason]

Charles, I haven't figured this out yet, but I get different results between our algos when the number of occurrences (nOccur in your function) exceeds the number present in the string, and even more perplexing, differences when used as in the example below:

FOR i = 1 TO 100
     fInstr(0, s, "cat", i AND 3, "dog")
     qReplace(s, "cat", i AND 3, "dog")    'replace with "dog"
NEXT

[Michael Mattias]

In subject example "I and 3" will never equal anything but 0, 1, 2 or 3 (boolean AND).

Zero has GOT to be causing grief somewhere.

Unless "I and 3" is being evaluated as ((ISTRUE I) AND (ISTRUE 3)), in which case it will always equal -1 when I ranges from 1 to 100. I'll bet minus-one is even worse grief than would be zero.

[Charles Dietz]

I'm afraid I wasn't very careful... STRIKE 1!
Here's another swing at the ball. Hopefully, it will be a base hit.

FUNCTION fInstr(start AS LONG, s AS STRING, t AS STRING, nOccur AS LONG, repl AS STRING) AS LONG
   LOCAL i, m, mm AS LONG
   mm = start
   FOR i = 1 TO nOccur
      m = INSTR(mm, s, t): IF m = 0 THEN EXIT FOR ELSE mm = m + LEN(t)
      IF i = nOccur THEN s = LEFT$(s, m - 1) + repl + MID$(s, mm)
   NEXT i
   FUNCTION = m
END FUNCTION

FUNCTION PBMAIN
   LOCAL s, ss, t AS STRING, k AS LONG
   LOCAL m, mm, n, i AS LONG
   s = "blackcat, white cat ,blue cat, what is a cat?, yadda yadda"
   k = fInstr(1, s, "cat", 2, "dog")
   MSGBOX s 
END FUNCTION

[Cliff Nichols]

I figured as much....I need to write wrappers to the simple Extract, and Replace functions...(No biggie, but thats why I asked to begin with so not to re-write the "Proverbial Wheel")

Nice to see the exchange of ideas though

[Michael Mattias]

need to write wrappers to the simple Extract, and Replace functions

A Real Man would use a regular expression.

Actually the REGEXPR code you need for this is in the demo I posted at REGEXPR and REGREPL demo January 16, 2002

All ya gots to do is tap in to the REGEXPR/REGREPL loops shown to increment and test an integer occurrence number and exit when appropriate.

(Cliff, I only give you a hard time because I think you show promise and a little challenge might just bring it out).

MCM