- print_r: documentation ( source)
- array_merge: documentation ( source)
- array_fill_keys: documentation ( source)
- array_diff: documentation ( source)
<?php
$arr1 = array(
"0" => 5,
"1" => 2,
"4" => 67
);
$arr2 = array(
"0" => 5,
"1" => 2,
"8" => 78
);
array_merge($arr2, array_fill_keys(array_diff($arr1, $arr2), 0));
print_r($arr2);