- array_merge_recursive: documentation ( source)
- print_r: documentation ( source)
<?php
$a1=array("a"=>"red","b"=>"green");
$a2=array("c"=>"blue","b"=>"yellow");
$c = array_merge_recursive($a1,$a2);
$a3=array("c"=>"blue","b"=>"yellow");
print_r(array_merge_recursive($a3,$c));