Re: A function to count all ocurrences of a character within a string.

On Mon, Mar 07, 2011 at 02:08:10PM -0800, bricklen wrote:
> On Mon, Mar 7, 2011 at 1:20 PM, Piotr Czekalski <pczekalski@techbaza.pl> wrote:
> > Hello pgsql community,
> >
> > Is there any string function (other than regex / scan & compare loop) to
> > obtain a list (or even a count) of characters within a string?
> > strpos and position seems to return only first occurence of a char/string
> > within substring.
> > The goal is to check if a string contains equal number of opening and
> > closing parenthesis, and if there are any of them.
> >
> > Regards,
> >
> > Piotr Czekalski
> 
> Couple examples here that might help to get you started
> http://www.postgres.cz/index.php/PostgreSQL_SQL_Tricks#Get_count_of_substrings_in_string

Oh, I like that trick! A little substitution and rearranging leads to:

CREATE OR REPLACE FUNCTION balanced_parens(text)
RETURNS integer AS $$SELECT(length(replace($1, '(', '')) - length(replace($1,')',''))) ;
$$ LANGUAGE SQL IMMUTABLE;

Generalizing (curly braces? brackets?)

CREATE OR REPLACE FUNCTION balanced_pairs(text,text,text)
RETURNS integer AS $$SELECT(length(replace($1, $2, '')) - length(replace($1,$3,''))) ;
$$ LANGUAGE SQL IMMUTABLE;

Ross
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Ross Reedstrom, Ph.D.                                 reedstrm@rice.edu
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