Combine arrays on value

Question

I have two arrays that look like this:

[
    ['id' => '1', 'color'=>'Green'],
    ['id' => '2', 'color'=>'Red'],
    ['id' => '3', 'color'=>'Blue'],
]

and

[
    ['id' => '2', 'size'=>'Small'],
    ['id' => '3', 'size'=>'Medium'],
    ['id' => '4', 'size'=>'Large'],
]

I would like to combine them on the value of the 'id' to produce:

[
    ['id' => '1', 'color'=>'Green', 'size'=>NULL],
    ['id' => '2', 'color'=>'Red', 'size'=>'Small'],
    ['id' => '3', 'color'=>'Blue','size'=>'Medium'],
    ['id' => '4', 'color'=>NULL, 'size'=>'Large'],
]

Note that both arrays may contain the same OR different 'id' values and would like all of the 'id's in the final array.

I have looked at array_merge and array_combine but neither seem to do the job.

Your help is appreciated

Answer 1

You can use array_merge() and isset():

$arr_a = [
    ['id' => '1', 'color' => 'Green'],
    ['id' => '2', 'color' => 'Red'],
    ['id' => '3', 'color' => 'Blue'],
];

$arr_b = [
    ['id' => '2', 'size' => 'Small'],
    ['id' => '3', 'size' => 'Medium'],
    ['id' => '4', 'size' => 'Large'],
];

$res = [];

foreach ($arr_a as $item) {
    $id = $item['id'];
    $res[$id] = $item;
    $res[$id]['size'] = NULL;
}

foreach ($arr_b as $item) {
    $id = $item['id'];
    if (isset($res[$id])) {
        $res[$id] = array_merge($res[$id], $item);
    } else {
        $res[$id] = $item;
        $res[$id]['color'] = NULL;
    }
}

print_r(array_values($res));

Prints

Array
(
    [0] => Array
        (
            [id] => 1
            [color] => Green
            [size] => 
        )

    [1] => Array
        (
            [id] => 2
            [color] => Red
            [size] => Small
        )

    [2] => Array
        (
            [id] => 3
            [color] => Blue
            [size] => Medium
        )

    [3] => Array
        (
            [id] => 4
            [size] => Large
            [color] => 
        )

)