Re: Very Stupid Regex question
On Thu, 07 Aug 2014 16:05:16 +, seany wrote:
obviously there are ways like counting the match length, and then using
the maximum length, instead of breaking as soon as a match is found.
Are there any other better ways?
You're not really using regexes properly. You want to greedily match as
much as possible in this case, e.g.:
void main()
{
import std.regex;
auto re = regex(ab(cd)?);
assert(PREabcdPOST.matchFirst(re).hit == abcd);
assert(PREabPOST.matchFirst(re).hit == ab);
}
Re: Very Stupid Regex question
On Thursday, 7 August 2014 at 16:05:17 UTC, seany wrote:
Cosider please the following:
string s1 = PREabcdPOST;
string s2 = PREabPOST;
string[] srar = [ab, abcd];
// this can not be constructed with a particular order
foreach(sr; srar)
{
auto r = regex(sr; g);
auto m = matchFirst(s1, r);
break;
// this one matches ab
// but I want this to match abcd
// and for s2 I want to match ab
}
obviously there are ways like counting the match length, and
then using the maximum length, instead of breaking as soon as a
match is found.
Are there any other better ways?
It's not clear to me what exactly you want, but:
Are the regexes in `srar` related? That is, does one regex always
include the previous one as a prefix? Then you can use optional
matches:
/ab(cd)?/
This will match abcd if it is there, but will also match ab
otherwise.
Re: Very Stupid Regex question
On Thursday, 7 August 2014 at 16:12:59 UTC, Justin Whear wrote:
On Thu, 07 Aug 2014 16:05:16 +, seany wrote:
obviously there are ways like counting the match length, and
then using
the maximum length, instead of breaking as soon as a match is
found.
Are there any other better ways?
You're not really using regexes properly. You want to greedily
match as
much as possible in this case, e.g.:
void main()
{
import std.regex;
auto re = regex(ab(cd)?);
assert(PREabcdPOST.matchFirst(re).hit == abcd);
assert(PREabPOST.matchFirst(re).hit == ab);
}
thing is, abcd is read from a file, and in the compile time, i
dont know if cd may at all be there or not, ir if it should be
ab(ef)
Re: Very Stupid Regex question
On Thu, Aug 07, 2014 at 04:49:05PM +, seany via Digitalmars-d-learn wrote:
On Thursday, 7 August 2014 at 16:12:59 UTC, Justin Whear wrote:
On Thu, 07 Aug 2014 16:05:16 +, seany wrote:
obviously there are ways like counting the match length, and then
using the maximum length, instead of breaking as soon as a match is
found.
Are there any other better ways?
You're not really using regexes properly. You want to greedily match
as much as possible in this case, e.g.:
void main()
{
import std.regex;
auto re = regex(ab(cd)?);
assert(PREabcdPOST.matchFirst(re).hit == abcd);
assert(PREabPOST.matchFirst(re).hit == ab);
}
thing is, abcd is read from a file, and in the compile time, i dont
know if cd may at all be there or not, ir if it should be ab(ef)
So basically you have a file containing regex patterns, and you want to
find the longest match among them?
One way to do this is to combine them at runtime:
string[] patterns = ... /* read from file, etc. */;
// Longer patterns match first
patterns.sort!((a,b) = a.length b.length);
// Build regex
string regexStr = %((%(%c%))%||%).format(patterns);
auto re = regex(regexStr);
...
// Run matches against input
char[] input = ...;
auto m = input.match(re);
auto matchedString = m.captures[0];
T
--
When solving a problem, take care that you do not become part of the problem.
Re: Very Stupid Regex question
On Thu, 07 Aug 2014 10:22:37 -0700, H. S. Teoh via Digitalmars-d-learn wrote: So basically you have a file containing regex patterns, and you want to find the longest match among them? // Longer patterns match first patterns.sort!((a,b) = a.length b.length); // Build regex string regexStr = %((%(%c%))%||%).format (patterns); auto re = regex(regexStr); This only works if the patterns are simple literals. E.g. the pattern 'a +' might match a longer sequence than 'aaa'. If you're out for the longest possible match, iteratively testing each pattern is probably the way to go.
Re: Very Stupid Regex question
On Thu, Aug 07, 2014 at 05:33:42PM +, Justin Whear via Digitalmars-d-learn wrote: On Thu, 07 Aug 2014 10:22:37 -0700, H. S. Teoh via Digitalmars-d-learn wrote: So basically you have a file containing regex patterns, and you want to find the longest match among them? // Longer patterns match first patterns.sort!((a,b) = a.length b.length); // Build regex string regexStr = %((%(%c%))%||%).format (patterns); auto re = regex(regexStr); This only works if the patterns are simple literals. E.g. the pattern 'a +' might match a longer sequence than 'aaa'. If you're out for the longest possible match, iteratively testing each pattern is probably the way to go. Hmm, you're right. I was a bit disappointed to find out that the | operator in std.regex (and also in Perl's regex) doesn't do longest-match but first-match. :-( I had always thought it did longest-match, like in lex/flex. I wish we can extend std.regex to allow longest-match for alternations... but there may be performance consequences. T -- There's light at the end of the tunnel. It's the oncoming train.
Re: Very Stupid Regex question
On Thu, Aug 07, 2014 at 10:42:13AM -0700, H. S. Teoh via Digitalmars-d-learn wrote: [...] Hmm, you're right. I was a bit disappointed to find out that the | operator in std.regex (and also in Perl's regex) doesn't do longest-match but first-match. :-( I had always thought it did longest-match, like in lex/flex. I wish we can extend std.regex to allow longest-match for alternations... but there may be performance consequences. https://issues.dlang.org/show_bug.cgi?id=13268 T -- Valentine's Day: an occasion for florists to reach into the wallets of nominal lovers in dire need of being reminded to profess their hypothetical love for their long-forgotten.
Re: Very Stupid Regex question
On Thursday, 7 August 2014 at 18:16:11 UTC, H. S. Teoh via Digitalmars-d-learn wrote: https://issues.dlang.org/show_bug.cgi?id=13268 T Thank you soo much!!
