PHP: Removing duplicate words from between quotes

Question

How can I remove the duplicates from between class="" in the following string?

<li class="active active"><a href="http://netcoding.net/indev/sample-page/">Sample Page</a></li>

Please note that the classes shown can change and be in different positions.

The real problem to solve is why you have duplicates in the first place! — Sparky, Apr 02 '14 at 16:31
So this is *almost certainly* not going to be possible with Regex. You are really going to have to *parse* this string. — Mike Perrenoud, Apr 02 '14 at 16:31
The OP is a classic example of the "XY Problem": http://meta.stackexchange.com/a/66378/157574 — Sparky, Apr 02 '14 at 16:36
You're not looking to "remove duplicate words from between quotes". You want to "remove duplicate words from the class attribute of an HTML
What @Sparky said. Please don't try and solve a symptom, solve the underlying problem instead. — ScottMcGready, Apr 08 '14 at 14:49

score 7 · Accepted Answer · answered Apr 02 '14 at 16:31

7

You can use DOM parser then explode and array_unique:

$html = '<li class="active active">
         <a href="http://netcoding.net/indev/sample-page/">Sample Page</a></li>';
$doc = new DOMDocument();
libxml_use_internal_errors(true);
$doc->loadHTML($html); // loads your html
$xpath = new DOMXPath($doc);
$nodelist = $xpath->query("//li");
for($i=0; $i < $nodelist->length; $i++) {
    $node = $nodelist->item($i);
    $tok = explode(' ', $node->getAttribute('class'));
    $tok = array_unique($tok);
    $node->setAttribute('class', implode(' ', $tok));
}
$html = $doc->saveHTML();
echo $html;

OUTPUT:

<html><body>
<li class="active"><a href="http://netcoding.net/indev/sample-page/">Sample Page</a></li>
</body></html>

Online Demo

answered Apr 02 '14 at 16:31

anubhava

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This is the first time I see you answer with DOM :) +1 – Shankar Damodaran Apr 02 '14 at 16:32
2

lol :) I am not a PHP programmer by profession but I have answered many using DOM in the past. – anubhava Apr 02 '14 at 16:33
This leaves empty class attributes. – Brian Graham Apr 02 '14 at 16:34
@BrianGraham, Seems like preventing the duplicates in the first place would be far less work. – Sparky Apr 02 '14 at 16:34
2

@BrianGraham, Nope see the demo here https://eval.in/130904 The code works perfect. – Shankar Damodaran Apr 02 '14 at 16:35
@BrianGraham I have attached generated output also which has one "active" – anubhava Apr 02 '14 at 16:35
1

@ShankarDamodaran: Thanks so much for your demo link, I took the liberty to include it in my answer. – anubhava Apr 02 '14 at 16:36

score 2 · Answer 2 · edited May 23 '17 at 11:57

With regex you could use a lookbehind and lookahead for finding duplicates:

$pattern = '/(?<=class=")(?:([-\w]+) (?=\1[ "]))+/i';

This would replace multiple instances of capture group 1 ([-\w]+) in a sequence.

$str = '<li class="active active">';

echo preg_replace($pattern, "", $str);

output:

<li class="active">

Test at regex101

EDIT 08.04.2014

To remove duplicates, that are not directly after the lookbehind (?<=class=")...

The problem is, that a lookbehind assertion can only be of fixed length. so something like (?<=class="[^"]*?) is not possible. As an alternative \K could be used, which resets the beginning of the match. A pattern could be:

$pattern = '/class="[^"]*?\K(?<=[ "])(?:([-\w]+) (?=\1[ "]))+/i';

You could imagine everything before \K as a virtual lookbehind of variable length.

This regex, as the first one, would only replace multiple instances of one duplicate in a sequence.

EDIT 11.09.2014

Finally I think a single regex, that would strip out all of different duplicates is getting rather complex:

/(?>(?<=class=")|(?!^)\G)(?>\b([-\w]++)\b(?=[^"]*?\s\1[\s"])\s+|[-\w]+\s+\K)/

This one uses continuous matching, as soon class=" is found.

Test at regex101; Also see SO Regex FAQ

A more simple way using regex would be a preg_replace_callback():

$html = '<li class="a1 a1 li li-home active li li active a1">';

$html = preg_replace_callback('/\sclass="\K[^"]+/', function ($m) {
  return trim(implode(" ",array_unique(preg_split('~\s+~', $m[0]))));
}, $html);

Note that older PHP-versions don't support anonymous functions (if so, change to a normal function).

How can I modify this so that it works with `li li-home active active`. It's stripping my `li`, and not any other repeating terms. — Brian Graham, Apr 08 '14 at 03:24
Hey @BrianGraham, see my updated answer. Also added a hyphen to the allowed classname characters `[-\w]` and `[ "]` as boundaries. — Jonny 5, Apr 08 '14 at 12:58

score 1 · Answer 3 · answered Apr 02 '14 at 16:39

A way to do it would be to add these values into an array and to filter them. Here is how it can be made.

<?php
   preg_match_all('/class="([A-Za-z0-9 ]+)"/',$htmlString, $result);
   $classes = explode(" ",$result[0]);
   $classes = array_unique($classes);
   echo "<li class=\"".implode(" ",$classes)."\"><a href=\"http://netcoding.net/indev/sample-page/\">Sample Page</a></li>";
?>

PHP: Removing duplicate words from between quotes

3 Answers3

OUTPUT:

Online Demo