PHP array merging

merge.php

<?php

// Non-associative.
$a = [1, 2, 3];
$b = [4, 5, 6, 7];

$c = $a + $b;
var_dump($c);

$d = array_merge($a, $b);
var_dump($d);

$a += $b;
var_dump($a);

echo '----' . PHP_EOL;

// Associative.
$a = ['one' => 1, 'two' => 2, 'three' => 3];
$b = ['one' => 4, 'two' => 5, 'three' => 6, 'four' => 7];

$c = $a + $b;
var_dump($c);

$d = array_merge($a, $b);
var_dump($d);

$a += $b;
var_dump($a);

Plus, you have to be careful about using string keys that "look" like integers.

// Associative (integer string keys, based on database row IDs).
$a = array('34987' => 1, '48907' => 2, '12039' => 3);
$b = array('34987' => 4, '48907' => 5, '12039' => 6, '89074' => 7);
$c = $a + $b;
var_dump($c);
$d = array_merge($a, $b);
var_dump($d);

array(4) { [34987]=> int(1) [48907]=> int(2) [12039]=> int(3) [89074]=> int(7) }
array(7) { [0]=> int(1) [1]=> int(2) [2]=> int(3) [3]=> int(4) [4]=> int(5) [5]=> int(6) [6]=> int(7) }