<!DOCTYPE html>
<html>
<body>
<?php
$a1=array("a"=>array("red"),"b"=>array("green","blue"),);
$a2=array("a"=>array("yellow"),"b"=>array("black"));
$result=array_replace_recursive($a1,$a2);
print_r($result);
$result=array_replace($a1,$a2);
print_r($result);
?>
</body>
</html>