PHP merge array by keys

Question

I have 2 arrays.

Array of goods and array of separators.

$goods = [
    [
        'good_id' => '1',
        'name' => 'Good 1',
    ],
    [
        'good_id' => '24',
        'name' => 'Good 24',
    ],
    [
        'good_id' => '335',
        'name' => 'Good 335',
    ],
    [
        'good_id' => '1986',
        'name' => 'Good 1986',
    ],
];

$separators = [
    [
        'id' => '1',
        'good_id' => '0',
        'name' => 'Separator 1',
    ],
    [
        'id' => '2',
        'good_id' => '0',
        'name' => 'Separator 2',
    ],
    [
        'id' => '3',
        'good_id' => '4',
        'name' => 'This separator should set after 4 good_id and before 5 good_id if exists',
    ],
    [
        'id' => '4',
        'good_id' => '47',
        'name' => 'This separator should set after 47 good_id and before 48 good_id if exists',
    ],
    [
        'id' => '5',
        'good_id' => '9999',
        'name' => 'This separator should set after 9999 good_id and before 10000 good_id if exists',
    ],
    [
        'id' => '6',
        'good_id' => '9999',
        'name' => 'This separator should set after 9999 good_id and AFTER prevously separator AND before 10000 good_id if exists',
    ]

];

I need to merge this arrays by good_id. Spearators good_id should sets after goods good_id by good_id.

$merged = [
    [
        'id' => '1',
        'good_id' => '0',
        'name' => 'Separator 1',
    ],
    [
        'id' => '2',
        'good_id' => '0',
        'name' => 'Separator 2',
    ],
    [
        'good_id' => '1',
        'name' => 'Good 1',
    ],
    [
        'id' => '3',
        'good_id' => '4',
        'name' => 'This separator should set after 4 good_id and before 5 good_id if exists',
    ],
    [
        'good_id' => '24',
        'name' => 'Good 24',
    ],
    [
        'id' => '4',
        'good_id' => '47',
        'name' => 'This separator should set after 47 good_id and before 48 good_id if exists',
    ],
    [
        'good_id' => '335',
        'name' => 'Good 335',
    ],
    [
        'good_id' => '1986',
        'name' => 'Good 1986',
    ],
    [
        'id' => '5',
        'good_id' => '9999',
        'name' => 'This separator should set after 9999 good_id and before 10000 good_id if exists',
    ],
    [
        'id' => '6',
        'good_id' => '9999',
        'name' => 'This separator should set after 9999 good_id and AFTER prevously separator AND before 10000 good_id if exists',
    ]

];

Answer 1

As far as I understood, you need to merge two arrays and sort the result by good_id sub key. Assuming these arrays doesn't have records with same good_id keys you may use this simple solution:

$merged = array_merge($goods, $separators);
usort($merged, function ($a, $b) {
    return $a['good_id'] < $b['good_id']? -1 : 1;
});