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
                )

        )

)

Stephen · Accepted Answer · 2010-11-22 17:44:23Z

9

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

edited Nov 22, 2010 at 17:44

answered Oct 25, 2010 at 21:30

Stephen

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4 Comments

Isis Over a year ago

how i can save a "key" matches? need "5,15,25,35", but have "0,1,2,3"

Stephen Over a year ago

You'll have to stop using array_merge. According to PHP docs, array_merge will always renumber numeric keys, even if you try using numbers in strings like array('1' => 'something', '2' => 'something');. In order to preserve keys, you'll have to use a + array union. I'll update my answer.

Isis Over a year ago

ru2.php.net/manual/en/function.array-merge-recursive.php#96201 find, thank you

Stephen Over a year ago

@Isis: Cool function! Useful for when you don't know the array's structure. But I would recommend a more surgical approach when you know exactly what structure you have, like in the problem at hand.

gen_Eric · Accepted Answer · 2010-10-25 21:31:47Z

4

Try using array_merge_recursive instead of array_merge.

answered Oct 25, 2010 at 21:31

gen_Eric

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Comments

Entity · Accepted Answer · 2010-10-25 21:30:01Z

0

Well, you could do it manually:

    $mergedArray = array();    

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

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

answered Oct 25, 2010 at 21:30

Entity

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1 Comment

M2tM Over a year ago

This will result in the exact same problem the original poster already has. In fact, he would get identical output to what he suggested he was trying to fix.

Spudley · Accepted Answer · 2010-10-25 21:30:15Z

0

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.

answered Oct 25, 2010 at 21:30

Spudley

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Comments

M2tM · Accepted Answer · 2010-10-25 21:31:35Z

0

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.

answered Oct 25, 2010 at 21:31

M2tM

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