PHP tag system with preg_match and foreach

Question

I'm trying to build this tag system for my website, where it checks the written article (could be 400-1000 words), for specific words and make a string with all the keywords found, from the array.

The one I made is working alright, but there is some problems I would like to fix.

$a = "This is my article and it's about apples and pears. I like strawberries as well though.";

$targets = array('apple', 'apples','pear','pears','strawberry','strawberries','grape','grapes');
foreach($targets as $t)
{
   if (preg_match("/\b" . $t . "\b/i", $a)) {
    $b[] = $t;
   }
}
echo $b[0].",".$b[1].",".$b[2].",".$b[3];
$tags = $b[0].",".$b[1].",".$b[2].",".$b[3];

First of all, I would like to know, if there is any way, I can make this more effecient. I have a database with around 5.000 keywords and expanding day by day.

A you can see, I don't know how to get ALL the matches. I'm writing $b[0], $b[1] etc.

I would like it to just make a string with ALL the matches - but only 1 time per match. If apples is mentioned 5 times, then only 1 should go in the string.

A said - this works. But I don't feel, that this is the best solution.

EDIT:

I'm now trying this, but I cant get it to work at all.

$a = "This is my article and it's about apples and pears. I like strawberries as well though.";

$targets = array('apple', 'apples','pear','pears','strawberry','strawberries','grape','grapes');
$targets = implode('|', $targets);
$b = [];
preg_match("/\b(" . $targets . ")\b/i", $a, $b);

echo $b;

Answer 1

preg_match already saves the matches. So:

int preg_match ( string $pattern , string $subject [, array &$matches [, int $flags = 0 [, int $offset = 0 ]]] )

The 3 param is already saving the matches, change this:

if (preg_match("/\b" . $t . "\b/i", $a)) {
    $b[] = $t;
}

To this:

$matches = [];
preg_match("/\b" . $t . "\b/i", $a, $matches);
$b = array_merge($b, $matches);

But, if you are comparing directly the word, the documentation recomends using strpos().

Tip
Do not use preg_match() if you only want to check if one string is contained in another string. Use strpos() instead as it will be faster.

---

EDIT

You could improve (in performance) your code if you still want to use preg_match by doing this, replace this:

$targets = array('apple', 'apples','pear','pears','strawberry','strawberries','grape','grapes');
foreach($targets as $t)
{
   if (preg_match("/\b" . $t . "\b/i", $a)) {
    $b[] = $t;
   }
}

With this:

$targets = array('apple', 'apples','pear','pears','strawberry','strawberries','grape','grapes');
$targets = implode('|', $targets);

preg_match("/\b(" . $t . ")\b/i", $a, $matches);

Here you are joining all your $targets with | (pipe), so your regex is like this: (target1|target2|target3|targetN) so you do only one search and not that foreach.