# content
Unicode Collation Sorting
Original Post

I recently added support to this website to receive Favourites and Replies through the ActivityPub posts that I create from each article.

Replies show up as comments after moderation, and favourites show up as Likes under each of the articles.

When fetching all the likes, my internal API returns the following structure — just like how PDOStatement::fetchAll() returns them:

array(7) {
  [0]=>
  array(8) {
    ["name"]=>
    string(14) "Marcus Bointon"
    ["linked_account"]=>
    string(33) "https://phpc.social/users/Synchro"
  }
  [1]=>
  array(8) {
    ["name"]=>
    string(14) "Derick Rethans"
    ["linked_account"]=>
    string(33) "https://phpc.social/users/derickr"
  }
  [2]=>
  array(8) {
    ["name"]=>
    string(26) "🇵🇸 Álvaro González"
    ["linked_account"]=>
    string(37) "https://mastodon.social/users/kAlvaro"
  }
}

I wanted to sort the likes by name, which turned out harder to be than I had hoped. Mostly because people do odd things with their names sometimes, such as not using an upper-case letter, or by prefixing their names with emojis as you can see in the example above.

If each entry in my array was only a string with a name, and no emoji is prefixed, you can use natcasesort(), but I have both complex objects and an emoji. This means PHP's built-in functions don't cut it.

However, PHP also has the extension, which has a Collator class with a sort method.

To create such a collator in code, use:

$collator = new Collator('root');

The Root Collation is ICU's Default Collation, but as the ICU documentation says:

This is good enough for my use case there, where I only want to sort names in a reasonable fashion.

One thing that it do is to sort lower-case letters before upper-case letters, but this behaviour can be changed by setting CASE_FIRST attribute on the collator to UPPER_FIRST:

$collator->setAttribute(Collator::CASE_FIRST, Collator::UPPER_FIRST);

Letters in non-Latin script will sort after the Latin letters.

However, the Collator->sort() method can only handle arrays of strings, and not complex objects.

To get around this limitation we instead use PHP's built-in usort() function with our own callback. In our callback we can use the Collator::getSortKey() method on each sort element's name array key to create the key that Collator::sort() would have used internally.

For good measure, we also use trim to remove preceding and trailing whitespace. The code to sort the elements now looks like:

$col = new Collator('root');
$col->setAttribute(Collator::CASE_FIRST, Collator::UPPER_FIRST);

usort(
    $allLikes,
    function($a, $b) use ($col) {
        $aName = trim($a['name']);
        $bName = trim($b['name']);
        $aKey = $col->getSortKey($aName);
        $bKey = $col->getSortKey($bName);

        return $aKey <=> $bKey;
    }
);

Now the only problem is that emojis sort before actual letters, so we need to scrub them. Each letter defined in the Unicode standard has properties associated with it. One of those properties is the General Category. If you examine the chart you will fined that for 0061;LATIN SMALL LETTER A the GC is Ll (Letter, Lower-case). The flag emoji from my example is composed of two characters: 1F1F5;REGIONAL INDICATOR SYMBOL LETTER P and 1F1F8;REGIONAL INDICATOR SYMBOL LETTER S. Both of these have as category So (Symbol, Other).

The PCRE library that PHP uses for regular expressions is aware of these categories, and you can select for for them with the \p{…} specifier. The documentation has a page on it.

In our case we want to remove all Symbols (with category S). Changing our trim lines to strip this character class accomplishes this.

When we now combine all of this, we get:

 'Marcus Bointon', 'linked_account' => 'https://phpc.social/users/Synchro' ],
    [ 'name' => 'Derick Rethans', 'linked_account' => 'https://phpc.social/users/derickr' ],
    [ 'name' => '🇵🇸 Álvaro González', 'linked_account' => 'https://mastodon.social/users/kAlvaro' ],
];

$col = new Collator('root');
$col->setAttribute(Collator::CASE_FIRST, Collator::UPPER_FIRST);

usort(
    $allLikes,
    function($a, $b) use ($col) {
        $aName = trim(preg_replace('/\p{S}+/u', '', $a['name']));
        $bName = trim(preg_replace('/\p{S}+/u', '', $b['name']));
        $aKey = $col->getSortKey($aName);
        $bKey = $col->getSortKey($bName);

        return $aKey <=> $bKey;
    }
);

var_dump($allLikes);
?>

When we now run the example with the $allLikes array from previously, our result is:

array(3) {
  [0] =>
  array(2) {
    'name' =>
    string(26) "🇵🇸 Álvaro González"
    'linked_account' =>
    string(37) "https://mastodon.social/users/kAlvaro"
  }
  [1] =>
  array(2) {
    'name' =>
    string(14) "Derick Rethans"
    'linked_account' =>
    string(33) "https://phpc.social/users/derickr"
  }
  [2] =>
  array(2) {
    'name' =>
    string(14) "Marcus Bointon"
    'linked_account' =>
    string(33) "https://phpc.social/users/Synchro"
  }
}

And from that, I can then generate the HTML code to render who liked my article, which you can hopefully see below.