Question

Is it possible to calculate with regex group matches?

String:

(00) Bananas
...
(02) Apples (red ones)
...
(05) Oranges
...
(11) Some Other Fruit
...

If the difference between the numbers at the beginning of each row is 3 or less, remove the “…” inbetween. So the string should be returned like this:

(00) Bananas
(02) Apples (red ones)
(05) Oranges
...
(11) Some Other Fruit

Regex:

$match = '/(*ANYCRLF)\((\d+)\) (.+)$
\.{3}
\((\d+)\) (.+)/m';

Now the tricky part is how to grab the matches and add some to a condition like

if($3-$1 >= 3) {
  //replace
}

Test: http://codepad.viper-7.com/f6iI4m

Thanks!

Answer 1

Here’s how you could do it with preg_replace_callback().

$callback = function ($match) {
    if ($match[3] <= $match[2] + 3) {
        return $match[1];
    } else {
        return $match[0];
    }
};

$newtxt = preg_replace_callback('/(^\((\d+)\).+$)\s+^\.{3}$(?=\s+^\((\d+)\))/m', $callback, $txt);

/(^\((\d+)\).+$)\s+^\.{3}$(?=\s+^\((\d+)\))/m

Here’s the pattern in pieces:

(^\((\d+)\).+$)      # subpattern 1, first line; subpattern 2, the number
\s+^\.{3}$           # newline(s) and second line ("...")
(?=\s+^\((\d+)\))    # lookahead that matches another numbered line 
                     # without consuming it; contains subpattern 3, next number

Thus, the entire pattern’s match is the first two lines (i.e., numbered line and ‘…’ line).

If the difference in numbers is greater than 3, replace with original text in $match[0] (i.e., no change). If difference is less than or equal to 3, replace with first line only (found in $match1]).