- var_dump: documentation ( source)
- array_merge: documentation ( source)
<?php
$array1 = array("id1" => "value1","id3" => "value6");
$array2 = array("id2" => "value2", "id3" => "value3", "id4" => "value4");
$array3 = array_merge($array2, $array1/*, $arrayN, $arrayN*/);
$array4 = $array1 + $array2;
echo '<pre>';
var_dump($array3);
var_dump($array4);
echo '</pre>';