Return arrays where arrays data inside them occurs only once

Given the following array of multiple arrays, I would like to return all arrays where their data isn't duplicated in other arrays. For example $a['test'] array should only contain arrays with keys 1,2,4,5,8 because their values aren't duplicated in other arrays. I am looking into array_filter function at the moment, but can't quite get it right. Thanks

$a['test'] = [
    1 => [
        'key_1' => 1,
        'key_2' => 2
    ],
    2 => [
        'key_1' => 7,
        'key_2' => 8
    ],
    3 => [
        'key_1' => 1,
        'key_2' => 2
    ],
    4 => [
        'key_1' => 5,
        'key_2' => 6
    ],
    5 => [
        'key_1' => 3,
        'key_2' => 4
    ],
    6 => [
        'key_1' => 1,
        'key_2' => 2
    ],
    7 => [
        'key_1' => 5,
        'key_2' => 6
    ],
    8 => [
        'key_1' => 9,
        'key_2' => 10
    ]
];

And this is how I would like the array to look like after processing

$a['test'] = [
    1 => [
        'key_1' => 1,
        'key_2' => 2
    ],
    2 => [
        'key_1' => 7,
        'key_2' => 8
    ],
    4 => [
        'key_1' => 5,
        'key_2' => 6
    ],
    5 => [
        'key_1' => 3,
        'key_2' => 4
    ],
    8 => [
        'key_1' => 9,
        'key_2' => 10
    ]
];

array_filter isn't terribly suited for this, because that looks at one array element at a time. You're better off loping over your input array and populating a helper array, where you use the combination of the key_1 and key_2 values as the key (encode them as JSON, to get a unique string value for each combination) - if an entry with the key combination for the current element already exists, then you don't add it again.

foreach($a['test'] as $item) {
    $key = json_encode($item);
    if(!isset($helper[$key])) {
        $helper[$key] = $item;
    }
}
$a['test'] = array_values($helper);;

print_r($a['test']);

Result:

Array
(
    [0] => Array
        (
            [key_1] => 1
            [key_2] => 2
        )

    [1] => Array
        (
            [key_1] => 7
            [key_2] => 8
        )

    [2] => Array
        (
            [key_1] => 5
            [key_2] => 6
        )

    [3] => Array
        (
            [key_1] => 3
            [key_2] => 4
        )

    [4] => Array
        (
            [key_1] => 9
            [key_2] => 10
        )

)

If you need to retain the original array's indexes in the result, then stick them into the data as well, so that you can restore them from there afterwards.

foreach($a['test'] as $akey => $item) {
    $key = json_encode($item);
    if(!isset($helper[$key])) {
        $helper[$key] = [$akey, $item];
    }
}
$a['test'] = array_combine(array_column($helper, 0), array_column($helper, 1));

print_r($a['test']);

Result:

Array
(
    [1] => Array
        (
            [key_1] => 1
            [key_2] => 2
        )

    [2] => Array
        (
            [key_1] => 7
            [key_2] => 8
        )

    [4] => Array
        (
            [key_1] => 5
            [key_2] => 6
        )

    [5] => Array
        (
            [key_1] => 3
            [key_2] => 4
        )

    [8] => Array
        (
            [key_1] => 9
            [key_2] => 10
        )

)