$string = '9,admin@google.com,8';
$array = explode(',', $string);

For more complicated situations, you may need to use preg_split.

Yes you can do this by using implode

$string = implode(', ', $tags);

And just so you know, there is an alias of implode, called join

$string = join(', ', $tags);

I tend to use join more than implode as it has a better name (a more self-explanatory name :D )

You can do this in Laravel 5.8 as follows:

DB::table('users')->select('username')->pluck('username')->unique()->flatten();

Hope this helps.

You can use the following solution:

$result = array();
foreach($inputArray as $value) {
    $result = array_merge($result, explode(',', $value));
}

Demo!

Original answer:

$arr = array('1,24,5', 4, '88, 12, 19, 6');
$result = array();

foreach ($arr as $value) {
    if(strpos($value, ',') !== FALSE) {
        $result = array_merge($result, explode(',', $value));
        $result = array_map('trim', $result); // trim whitespace
    }
    else {
        $result[] = trim($value);
    }
}

print_r($result);