如何通过php中的条件更新数组中的值？

Question

I have alt array like this :

$alt = array('chelsea', 'mu', 'arsenal');

I have photoList array like this :

$photoList = array(
    array(
        'id'    => 1,
        'name'  => 'chelsea.jpg',
        'alt'   => ''
    ),
    array(
        'id'    => 2,
        'name'  => 'mu.jpg',
        'alt'   => ''
    ),
    array(
        'id'    => 3,
        'name'  => 'arsenal.jpg',
        'alt'   => ''
    )
);

I want to check a condition

If index plus 1 in the alt array same with id in the photoList array, it will update alt in the photoList array with value of alt array by index plus 1

I try like this :

foreach($photoList as $key1 => $value1) {
    foreach ($alt as $key2 => $value2) {
        if($value1['id'] == $key2+1)
            $value1['alt'] = $value2;
    }
}

Then I check with :

echo '<pre>';print_r($photoList);echo '</pre>';

The alt is still empty. It does not update

I hope the result like this :

photoList = array(
    array(
        'id'    => 1,
        'name'  => 'chelsea.jpg',
        'alt'   => 'chelsea'
    ),
    array(
        'id'    => 2,
        'name'  => 'mu.jpg',
        'alt'   => 'mu'
    ),
    array(
        'id'    => 3,
        'name'  => 'arsenal.jpg',
        'alt'   => 'arsenal'
    )
);

How can I do it?

Answer 1

You have to use the vars ($value1) by reference :

                           // THIS & is the trick
foreach($photoList as $key1 => &$value1) {
    foreach ($alt as $key2 => $value2) {
        if($value1['id'] == $key2+1)
            $value1['alt'] = $value2;
    }
}

Without that you work with an 'internal copy' of the sub-item $value1 , so $photoList doesn't get updated.

Answer 2

A better approach will be to do that:

foreach($photoList as $key => $value)
    $photoList[$key]['alt'] = $alt[$key];

This way round you use only one loop. Also, what's wrong with your original loop is that you are assigning the value to the temporary variable inside the loop. This is not affecting the array you are looping over.

EDIT :

I just figured out that you do not need to care about $photoList[$key]['id'] at all. It's irrelevant in this example as the order of the elements is the same in both arrays.