PHP array_merge problem

Question

$a = array('matches' => 
        array(
            '5' => array('weight' => 6),
            '15' => array('weight' => 6),
        )
    );

    $b = array('matches' => 
        array(
            '25' => array('weight' => 6),
            '35' => array('weight' => 6),
        )
    );

    $merge = array_merge($a, $b);

    print_r($merge);

The result of this script is

Array
(
    [matches] => Array
        (
            [25] => Array
                (
                    [weight] => 6
                )

            [35] => Array
                (
                    [weight] => 6
                )

        )

)

But why?

I want the result was this:

Array
(
    [matches] => Array
        (
            [5] => Array
                (
                    [weight] => 6
                )

            [15] => Array
                (
                    [weight] => 6
                )
            [25] => Array
                (
                    [weight] => 6
                )

            [35] => Array
                (
                    [weight] => 6
                )

        )

) 

Answer 1

Because the key 'matches' in the first array is being overwritten by the same key in the second. You need to do this instead:

$merge = array('matches' => array());
$a = array(
    'matches' => array(
        '5' => array('weight' => 6),
        '15' => array('weight' => 6)
    )
);

$b = array(
    'matches' => array(
        '25' => array('weight' => 6),
        '35' => array('weight' => 6)
    )
);

$merge['matches'] = array_merge($a['matches'], $b['matches']);

print_r($merge);

UPDATE

In order to preserve the numeric keys, you'll have to do this:

$merge['matches'] = $a['matches'] + $b['matches'];

If using the array union operator like this, just remember the following from php.net:

The keys from the first array will be preserved. If an array key exists in both arrays, then the element from the first array will be used and the matching key's element from the second array will be ignored.

http://php.net/manual/en/function.array-merge.php

Answer 2

Try using array_merge_recursive instead of array_merge.

Answer 3

You're merging the top-level of the array. The array_merge() function is seeing that they both contain a "matches" element, so it is picking one as the merged result.

If you want it to scan deeper, you need to run array_merge() at the next level down in the array. In this case it's relatively simple because you only have one element at the top level of each array, so you'd only need a single line - Something like this:

$merge['matches'] = array_merge($a['matches'], $b['matches']);

A more complex array structure would need more work, though.

Hope that helps.

Answer 4

Try:

$merge = array();
$merge['matches'] = array_merge($a['matches'], $b['matches']);

Your problem is that you are merging the top level $a array with $b and both of these have a "matches" index so it's accepting $b's version of that element. You can get around this by explicitly merging in that index's array ($a['matches'] with $b['matches']) and assigning it to the merged array ($merge['matches']) which will result in the expected behavior.

Alternatively array_merge_recursive will do what you want.

Answer 5

Well, you could do it manually:

    $mergedArray = array();    

    foreach($a as $key => $value)
    {
        $mergedArray[$key] = $value;
    }

    foreach($b as $key => $value)
    {
        $mergedArray[$key] = $value;
    }