topic Re: Find position of end/matching Bracket in SAS Programming

Find position of end/matching Bracket

kyle1190 — Thu, 20 Jan 2022 19:59:54 GMT

Hi All,

I am trying to come up with a way to scan strings and locate the matching end bracket to the first parent bracket. The difficult part is that there may be many levels of nested brackets within and/or adjacent to the bracket pair of interest. I am not as familiar with perl regular expressions but after doing some searching seems like it may be one potential path to take? Or some tedious do-looping?

Note, the first character of the string will always be the parent bracket of interest. Additionally there will always be an even number of { and }. For example, have:

data have;
length HAVE $50.;
	input HAVE $;
	datalines;
{}
{{}{}{}{}{}}
{{}{}{}{}{{}}}{}
{{}{{{}}}{}{}{{}}}{}{{}}
;run;

Here I have manually bold the matching end bracket of interest for clarity:

{}

{{}{}{}{}{}}

{{}{}{}{}{{}}}{}

{{}{{{}}}{}{}{{}}}{}{{}}

Want:

12;

14;

18;

Thank you

Re: Find position of end/matching Bracket

ballardw — Thu, 20 Jan 2022 20:09:48 GMT

If you are trying to read data from a file it may help to provide some information about that. This sounds like it may possibly be JSON, in which case you might want to use a LIBNAME with the JSON engine to read the data instead of writing a bunch of, quite possibly complex and fragile, code.

@kyle1190 wrote:

Hi All,

I am trying to come up with a way to scan strings and locate the matching end bracket to the first parent bracket. The difficult part is that there may be many levels of nested brackets within and/or adjacent to the bracket pair of interest. I am not as familiar with perl regular expressions but after doing some searching seems like it may be one potential path to take? Or some tedious do-looping?

Note, the first character of the string will always be the parent bracket of interest. Additionally there will always be an even number of { and }. For example, have:
data have;
length HAVE $50.;
	input HAVE $;
	datalines;
{}
{{}{}{}{}{}}
{{}{}{}{}{{}}}{}
{{}{{{}}}{}{}{{}}}{}{{}}
;run;
Here I have manually bold the matching end bracket of interest for clarity:

{}

{{}{}{}{}{}}

{{}{}{}{}{{}}}{}

{{}{{{}}}{}{}{{}}}{}{{}}

Want:

2;

12;

14;

18;

Thank you

Re: Find position of end/matching Bracket

kyle1190 — Thu, 20 Jan 2022 21:38:17 GMT

Hi ballardw,
Thanks for the quick response. Not JSON, actually in this case I am trying to parse some RTF files read in as text lines in order to make some minor adjustments and then recreate the RTF files. I would be okay with somewhat lengthy code, if necessary.

Thank you

Re: Find position of end/matching Bracket

ballardw — Thu, 20 Jan 2022 22:04:57 GMT

This seems to find the matches for your example data. You could likely drop the i,open and close variables after testing. If you have not seen it before the LEAVE instruction exits a loop on execution so this quits when the match is found.

data want;
   set have;
   /* assumes we are matching the FIRST { character*/
   do i=1 to length(have);
      if substr(have,i,1)='{' then open= sum(open,1);
      if substr(have,i,1)='}' then close=sum(close,1);
      if open=close then do;
         matchposition=i;
         leave;
      end;
   end;
run;

@kyle1190 wrote:
Hi ballardw,
Thanks for the quick response. Not JSON, actually in this case I am trying to parse some RTF files read in as text lines in order to make some minor adjustments and then recreate the RTF files. I would be okay with somewhat lengthy code, if necessary.

Thank you