Retain rows in a 2d array which are not found in another 2d array

Question

I've got two two-dimensional arrays and I need to filter the first array's rows by the second array's rows.

$array1 = [
    ["module1", "path/to/file.txt", ""],
    ["module2", "path/to/file2.txt", ""],
];

$array2 = [
    ["module1", "path/to/file.txt", ""]
];

I would think that doing array_diff($array1, $array2) would give me where the first array's rows were not found in the second array, but I got an empty array.

I tried switching the parameters, and still produced an empty array, but this time without surprise. Can array_diff not be used on arrays of arrays?

Answer 1

From the documentation:

Two elements are considered equal if and only if (string) $elem1 === (string) $elem2. In words: when the string representation is the same.

echo (string) array(); gives you just Array, so for array_diff, your arrays look like:

$array1 = array('Array', 'Array');
$array2 = array('Array');

---

So to create a diff for your arrays, you would need something like this (assuming that every element in the arrays is itself an array):

$diff = array();

foreach($array1 as $val1) {
    $contained = false;
    foreach($array2 as $val2) {
        if(count(array_diff($val1, $val2)) == 0) {
            $contained = true; 
            break;
        }
    }
    if(!$contained) {
        $diff[] = $val1;
    }
}

Disclaimer: This is more or less just a sketch.

Answer 2

From the array_diff documentation.

This function only checks one dimension of a n-dimensional array. Of course you can check deeper dimensions by using array_diff($array1[0], $array2[0]);

Answer 3

From the array_diff manual page: "This function only checks one dimension of a n-dimensional array. Of course you can check deeper dimensions by using array_diff($array1[0], $array2[0]);."

Answer 4

To compare the rows between two 2d arrays, use array_udiff() using the 3-way comparison operator (spaceship operator).

Code: (Demo)

var_export(
    array_udiff($array1, $array2, fn($a, $b) => $a <=> $b)
);

Fun facts:

• 2005-11-24: array_udiff was added to PHP (v5.1).
• 2015-12-03: The spaceship operator (<=>) was added to PHP (v7).
• 2019-11-28: Arrow function syntax (fn() =>) was added to PHP (v7.4).