- array_map: documentation ( source)
- implode: documentation ( source)
- array_keys: documentation ( source)
<?php
$input = array('aaa' => '111', 'bbb' => '222');
$output = implode(', ', array_map(function ($v, $k) { return $k . '=' . $v; }, $input, array_keys((array)$input)));
echo $output;