PHP and RegEx: Split a string by commas that are not inside brackets (and also nested brackets)

Question

Two days ago I started working on a code parser and I'm stuck.

How can I split a string by commas that are not inside brackets, let me show you what I mean:

I have this string to parse:

one, two, three, (four, (five, six), (ten)), seven

I would like to get this result:

array(
 "one"; 
 "two"; 
 "three"; 
 "(four, (five, six), (ten))"; 
 "seven"
)

but instead I get:

array(
  "one"; 
  "two"; 
  "three"; 
  "(four"; 
  "(five"; 
  "six)"; 
  "(ten))";
  "seven"
)

How can I do this in PHP RegEx.

Thank you in advance !

Answer 1

I am afraid that it could be very difficult to parse nested brackets like one, two, (three, (four, five)) only with RegExp.

Answer 2

You can't, directly. You'd need, at minimum, variable-width lookbehind, and last I knew PHP's PCRE only has fixed-width lookbehind.

My first recommendation would be to first extract parenthesized expressions from the string. I don't know anything about your actual problem, though, so I don't know if that will be feasible.

Answer 3

I can't think of a way to do it using a single regex, but it's quite easy to hack together something that works:

function process($data)
{
        $entries = array();
        $filteredData = $data;
        if (preg_match_all("/\(([^)]*)\)/", $data, $matches)) {
                $entries = $matches[0];
                $filteredData = preg_replace("/\(([^)]*)\)/", "-placeholder-", $data);
        }

        $arr = array_map("trim", explode(",", $filteredData));

        if (!$entries) {
                return $arr;
        }

        $j = 0;
        foreach ($arr as $i => $entry) {
                if ($entry != "-placeholder-") {
                        continue;
                }

                $arr[$i] = $entries[$j];
                $j++;
        }

        return $arr;
}

If you invoke it like this:

$data = "one, two, three, (four, five, six), seven, (eight, nine)";
print_r(process($data));

It outputs:

Array
(
    [0] => one
    [1] => two
    [2] => three
    [3] => (four, five, six)
    [4] => seven
    [5] => (eight, nine)
)

Answer 4

Clumsy, but it does the job...

<?php

function split_by_commas($string) {
  preg_match_all("/\(.+?\)/", $string, $result); 
  $problem_children = $result[0];
  $i = 0;
  $temp = array();
  foreach ($problem_children as $submatch) { 
    $marker = '__'.$i++.'__';
    $temp[$marker] = $submatch;
    $string   = str_replace($submatch, $marker, $string);  
  }
  $result = explode(",", $string);
  foreach ($result as $key => $item) {
    $item = trim($item);
    $result[$key] = isset($temp[$item])?$temp[$item]:$item;
  }
  return $result;
}


$test = "one, two, three, (four, five, six), seven, (eight, nine), ten";

print_r(split_by_commas($test));

?>

Answer 5

Hm... OK already marked as answered, but since you asked for an easy solution I will try nevertheless:

<?php
  $test = "one, two, three, , , ,(four, five, six), seven, (eight, nine)";
  $split = "/([(].*?[)])|(\w)+/";
  preg_match_all($split, $test, $out);
  print_r($out[0]);              
  die();
?>

Output

Array
(
    [0] => one
    [1] => two
    [2] => three
    [3] => (four, five, six)
    [4] => seven
    [5] => (eight, nine)
)

Answer 6

You can do that easier:

preg_match_all('/[^(,\s]+|\([^)]+\)/', $str, $matches)

But it would be better if you use a real parser. Maybe something like this:

$str = 'one, two, three, (four, (five, six), (ten)), seven';
$buffer = '';
$stack = array();
$depth = 0;
$len = strlen($str);
for ($i=0; $i<$len; $i++) {
    $char = $str[$i];
    switch ($char) {
    case '(':
        $depth++;
        break;
    case ',':
        if (!$depth) {
            if ($buffer !== '') {
                $stack[] = $buffer;
                $buffer = '';
            }
            continue 2;
        }
        break;
    case ' ':
        if (!$depth) {
            continue 2;
        }
        break;
    case ')':
        if ($depth) {
            $depth--;
        } else {
            $stack[] = $buffer.$char;
            $buffer = '';
            continue 2;
        }
        break;
    }
    $buffer .= $char;
}
if ($buffer !== '') {
    $stack[] = $buffer;
}
var_dump($stack);

Answer 7

I feel that its worth noting, that you should always avoid regular expressions when you possibl can. To that end, you should know that for PHP 5.3+ you could use *str_getcsv()*. However, if you're working with files (or file streams), such as CSV files, then the function fgetcsv() might be what you need, and its been available since PHP4.

Lastly, I'm surprised nobody used preg_split(), or did it not work as needed?