Merging two multidimensional arrays on specific key

Question

Let\'s say I have following arrays:

Array
    (
        [0] => Array
            (
                [id] => 5
                [name] => Education
            


        

Answer 1

This can be easily done using the 3-parameter form of array_column to re-index your second array by the id value and then looping over the first array, merging the contents of the matching second value (where it exists):

$second = array_column($second, null, 'id');
foreach ($first as &$subject) {
    $subject = array_merge($subject, $second[$subject['id']] ?? []);
}

Output:

Array
(
    [0] => Array
        (
            [id] => 5
            [name] => Education
            [title] => Edu
        )
    [1] => Array
        (
            [id] => 4
            [name] => Computers
            [title] => Comp
        )
    [3] => Array
        (
            [id] => 7
            [name] => Science
            [title] => Sci
        )
    [4] => Array
        (
            [id] => 1
            [name] => Sports
            [title] => Sport
        )
)

Demo on 3v4l.org

This has the advantage over Will B.'s answer of not re-indexing the first array. It's also slightly faster (my tests show ~10%) due to only having one call to array_column and none to array_values.

Update

This code can actually be sped up even more by using the array union operator (+) (thanks @mickmackusa):

$second = array_column($second, null, 'id');
foreach ($first as &$subject) {
    $subject += $second[$subject['id']] ?? [];
}

The output of this code is the same as above, but it runs about 10% faster again.

Demo on 3v4l.org