Re: PCRE: references to captures in replace string

4 May 2016

      Another option is to use R. This is available in Jul2015 branch, and is
very easy (https://www.monetdb.org/content/embedded-r-monetdb)

CREATE FUNCTION r_replace(s STRING, p STRING, r STRING) RETURNS STRING
LANGUAGE R {
 sub(p,r,s)
};

sql>select r_replace('Apple Pear', '^([a-zA-Z]+)\\s*([a-zA-Z]+)$', '\\2
\\1');
+------------------------+
| r_replace_single_value |
+========================+
| Pear Apple             |
+------------------------+

It works out of the box on columns:

select r_replace(value, '^.*(\d).*$','\\1%\\2') from obj_string limit 100;

And luckily without loops:

X_10:bat[:oid,:str] := batrapi.eval(nil,"{\n sub(p,r,s)\n};",X_9,A0,A1);

Still not very fast - I've just tried on 11M strings, 45s - probably
because strings are fully copied, but for now this seems the easiest
workaround.

It would be great to have it working on pcre though.
Roberto

On 4 May 2016 at 10:31, Roberto Cornacchia 
wrote:
...
An interesting workaround for now could be to implement a simple UDF in
python, to let python perform the regex processing:
https://www.monetdb.org/blog/embedded-pythonnumpy-monetdb
Unfortunately this is for now only available in a separate branch which is
kept in sync with default. For me this is no option because I need to rely
on a stable MonetDB version. But perhaps for other it is an option.
On 26 April 2016 at 16:57, imad hajj chahine 
wrote:
...
I still find this to be an interested feature to add, as its very useful
in string date manipulation.
On Tue, Apr 26, 2016 at 5:28 PM, Roberto Cornacchia <
roberto.cornacchia@gmail.com> wrote:
...
I found this thread from October 2015 where Sjoerd concludes that back
references replacement is not implemented in the MonetDB wrapper:
https://www.monetdb.org/pipermail/users-list/2015-October/008492.html
Probably that is still the case?
On 20 April 2016 at 16:35, Roberto Cornacchia <
roberto.cornacchia@gmail.com> wrote:
...
After declaring a wrapper for pcre.replace:
sql>create function pcre_replace(s string, pattern string, repl string,
flags string) returns string external name pcre."replace";
operation successful (6.187ms)
I cannot get replacements with references to captures work (but the
code in pcre.c seems to support it):
sql>select pcre_replace('Apple Pear', '^([a-zA-Z]+)\\s*([a-zA-Z]+)$',
'\\1 \\2', '');
+---------------------------+
| pcre_replace_single_value |
+===========================+
| \1 \2                     |
+---------------------------+
1 tuple (0.309ms)
The pattern is matched, but the back references are replaced literally.
Am I not getting the syntax correct?
From http://www.pcre.org/original/doc/html/pcresyntax.html I see I
could use any of \1, \g1, \g{1] for back references, but none seem to work.
Roberto
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