Something like charIndex, but in a variable...

[Peter Haworth]

For those whose eyes glaze over when looking at regexp, it seems Jacque's
suggestion of the offset function making use of the chars to skip easily
solves this problem.  I don;t have the original post in front of me so
can't remember if the objective was to find the last occurrence of the
character or the first and last.  This finds both.

on mouseUp

   put zero into tSkip
   repeat until tOffset is zero
         put offset("b",tVar,tSkip) into tOffset
         if tOffset <>0 then
               if tSkip is zero then
                     put tOffset into tStart
               else
                     put tSkip+tOffset into tEnd
               end if
               add tOffset to tSkip
         end if
   end repeat

end mouseUp

No idea on performance.  I've often thought it would be great if there was
a way for offset to start at the end of a string and work backwards, maybe
a "direction" parameter.




Pete
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On Thu, Apr 30, 2015 at 8:50 AM, Ben Rubinstein <benr_mc at cogapp.com> wrote:

> On 30/04/2015 09:07, Malte Brill wrote:
>
>> I need to find the start and end character of chuncks in a variable. If
>> we are in a field we can use charIndex for that. However, in a variable I
>> have no good idea on how to do something similar to
>>
>> get charIndex(token 7 of line 15 of field „myField“)
>>
>
> (unhelpful to Malte, sorry) - I hadn't noticed the introduction of
> charIndex.  What a useful property.  It would be great if it could be
> extended to arbitrary sources of value.
>
> In the meantime, could one write an ugly function to calculate the start
> index of a chunk by first getting the length of the preceeding chunks, then
> using that value as the charsToSkip for a call to offset on the value of
> the chunk?
>
> So a first approximation - it would need some better work parsing the
> chunk expression to be robust -
>
> function chunkIndex tFullChunkExpr, tValue
>    local tChunkExpr, tPriorChunksExpr, tChunkValue, iConsumed, n, i
>
>    -- convert nested chunk expression into lines, minor to major
>    replace " of " with return in tFullChunkExpr
>    if last word of tFullChunkExpr = "of" then \
>         delete last word of tFullChunkExpr
>
>    -- accumulate start of each level of chunk
>    put 0 into iConsumed
>
>    -- find the start of each chunk in the expression, from major to minor
>    repeat with i = number of lines in tFullChunkExpr down to 1
>       put line i of tFullChunkExpr into tChunkExpr
>
>       -- make an expression for the chunks prior to this one
>       put tChunkExpr into tPriorChunksExpr
>       put format("1 to %d", word 2 of tChunkExpr - 1) \
>             into word 2 of tPriorChunksExpr
>
>       -- get the length of the chunks prior to this one
>       do format("put length(%s of tValue) into n", tPriorChunksExpr)
>
>       -- get this chunk, and find the first instance
>       -- of it after the length of the prior chunks
>       do ("put" && tChunkExpr && "of tValue into tChunkValue")
>       add offset(tChunkValue, tValue, n) + n to iConsumed
>
>       -- repeat within this chunk
>       put tChunkValue into tValue
>    end repeat
>
>    return iConsumed - 1
> end chunkIndex
>
>
> To be called as e.g.
>    get chunkIndex("token 7 of line 15 of", myVar)
>
> I suspect that this could be fooled if there was a lot of leading white
> space (and a repetition of the target chunk prior to it), but that could
> probably be dealt with by an additional check for offset of the
> 'priorChunkValue'.
>
>
> Ben
>
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