Why can't I merge arrays using array_merge()?

Question

I'm unsuccessfully trying to merge arrays. An array looks like this:

//var_dump()
array (size=2)
  0 => 
    object(Brand)[177]
      (...)
  1 => 
    object(Brand)[271]
      (...)

This is the code I use:

        $premiumBrands = array();

        foreach ($stores as $store) :
            $brands = getBrands($store->brands);

            echo count($brands['premium']).', ';

            if(count($brands['premium']) > 0) {
                array_merge($premiumBrands,$brands['premium']);
            }
        endforeach;

        echo count(premiumBrands);

The result of the output in the loop is this: 2, 0, 0, 1, 0;
The result of the last output is this: 0;

Using

$premiumBrands = $premiumBrands + $brands['premium'];

will not work, because all arrays starts with an index key of [0] - so it will just overwrite premiumBrands

So how can I merge my arrays?

And yes, I've read the docs. Still can't solve it.

$premiumBrands = array_merge($premiumBrands, $brands['premium']);? array_merge returns a new array, it does not alter the existing ones. Read the docs - php.net/manual/en/function.array-merge.php — Bjorn
– Bjorn, Commented Jan 6, 2015 at 21:22
Yes @Bjorn, I've read the docs. Even tried $premiumBrands + $brands['premium']. See updated Q. — Steven
– Steven, Commented Jan 6, 2015 at 21:32
@Steven, you can't sum up arrays as you're trying to do in your updated question. Just replace the line with the code I gave you. The point you're missing is that array_merge returns a fresh array, but you have to assign it to a variable to keep it. array_merge does not alter any array you give it. — Bjorn
– Bjorn, Commented Jan 6, 2015 at 21:37

zgr024 · Accepted Answer · 2015-01-06 21:35:26Z

3

You need to assign the new array to a variable. The new array will contain the merged arrays which you can merge over and over in a loop. It all depends on what your keys and values are to get it to work the way you want, but the documentation is clear http://php.net/manual/en/function.array-merge.php

    $premiumBrands = array();

    foreach ($stores as $store) :
        $brands = getBrands($store->brands);

        echo count($brands['premium']).', ';

        if(count($brands['premium']) > 0) {
            $premiumBrands = array_merge($premiumBrands,$brands['premium']); /// *** ///
        }
    endforeach;

    echo count(premiumBrands);

answered Jan 6, 2015 at 21:35

zgr024

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2 Comments

Steven Over a year ago

Of course. At the end of the day my brain is mush and I thought array_merge did that job for me. #shouldnotworkwhentired

zgr024 Over a year ago

PHP is dirty like that. Some functions return the result, others manipulate the parameters, but in most cases, the result is returned.

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