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(at)techbaza(dot)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
--
Ross Reedstrom, Ph.D. reedstrm(at)rice(dot)edu
Systems Engineer & Admin, Research Scientist phone: 713-348-6166
Connexions http://cnx.org fax: 713-348-3665
Rice University MS-375, Houston, TX 77005
GPG Key fingerprint = F023 82C8 9B0E 2CC6 0D8E F888 D3AE 810E 88F0 BEDE