Re-order regular expression matches - php

Question

Is there a way to get the match patterns to change order? For example if you have a string with letters-digits and using preg_match_all(), and you want the resulting match array to have the digits before the letters. Is there a way to specify this in the regular expression itself?
So "aaa-111" would result in matches with
array(0 => '111', 1 => 'aaa');

Answer 1

Perhaps named capture groups will help. Example:
preg_match('/(?<alphapart>[a-z]+)-(?<numpart>[0-9]+)/', 'aaa-111', $matches);
$matches:
array('alphapart' => 'asd', 'numpart' => '111')
This way you can refer to the matches by a name instead of whatever order index they were matched in.
Edit: Just for accuracy, I want to note that $matches will actually include the matches by index as well, so the actual $matches will be: array(5) { [0]=> string(7) "aaa-111" ["alphapart"]=> string(3) "aaa" [1]=> string(3) "aaa" ["numpart"]=> string(3) "111" [2]=> string(3) "111" }

Answer 2

The order of groups in a regex is dependent on their positions in the regex and the string. Changing the order would make it very confusing.
What you can do is use "named groups".
/(?P<letters>\w*)-(?P<digits>\d*)/
The array will still be in the same order, but, you can use $matches['digits'] to easily get just the digits.
DEMO: http://ideone.com/3tRJLZ

Answer 3

Yes you can. You can use lookaheads that don't push the 'cursor' and so you could first match the last part, and then the first part. It works with (?=regex)
This works:
(?=\w+\-(\d+))(\w+)\-\d+
but will also give the full match at index 0. Like ["aaa-111", "111", "aaa"]
is that a problem?

Answer 4

I don't believe there is. Regex isn't designed to sort. You could setup two different regular expressions to check for each pattern though. This code will echo the two string in num/alpha order as you requested:
<?php
header('Content-Type: text/plain');
$string1 = 'aaa-123';
$string2 = '123-aaa';
echo 'String 1: '.$string1."\n";
echo 'String 2: '.$string2."\n";
$pattern1 = '/([\d]+)-([a-z]+)/i';
$pattern2 = '/([a-z]+)-([\d]+)/i';
echo 'Result 1: ';
if(preg_match($pattern1, $string1, $matches))
{
echo $matches[1].' '.$matches[2]."\n";
}
if(preg_match($pattern2, $string1, $matches))
{
echo $matches[2].' '.$matches[1]."\n";
}
echo 'Result 2: ';
if(preg_match($pattern1, $string2, $matches))
{
echo $matches[1].' '.$matches[2]."\n";
}
if(preg_match($pattern2, $string2, $matches))
{
echo $matches[2].' '.$matches[1]."\n";
}
?>
The resulting output is:
String 1: aaa-123
String 2: 123-aaa
Result 1: 123 aaa
Result 2: 123 aaa

Answer 5

If you want the digits to be there first, you need to sort the array yourself.
array_sort() will... sort it out for you.