- implode: documentation ( source)
- array_walk: documentation ( source)
<?php
$input = array(
array(
'tag_name' => array('google', 'Yahoo')
),
array(
'tag_name' => array('technology', 'andsuch')
)
);
echo implode(', ', array_walk(function ($entry) {
return $entry['tag_name'];
}, $input));