Why does array_diff on arrays of arrays return an empty array?

Question

I've got two arrays, for which var_dump give the following values:

$array1:

Artifacts:array(2) { [0]=>  array(3) { [0]=>  string(7) "module1" [1]=>  string(16) "path/to/file.txt" [2]=>  string(0) "" } [1]=>  array(3) { [0]=>  string(7) "module2" [1]=>  string(17) "path/to/file2.txt" [2]=>  string(0) "" } }

$array2:

Artifacts:array(1) { [0]=>  array(3) { [0]=>  string(7) "module1" [1]=>  string(16) "path/to/file.txt" [2]=>  string(0) "" } }

I would think that doing array_diff($array1,$array2) would give me an array countaining only the second elements. Instead I got an empty array. I try switching the parameters, and still an empty_array, but this time without surprise. Wouldn't array_diff work on arrays of arrays?

Felix Kling · Accepted Answer · 2011-02-10T10:19:16.983

6

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.

edited Feb 10 '11 at 10:19

answered Feb 10 '11 at 10:09

Felix Kling

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If I understand you correctly, I'll have to write my own function to see if there is any differences between the two arrays, am I right? – Eldros Feb 10 '11 at 10:14
@Eldros: Yes, you would have to loop over the "outer" arrays and use `array_diff` for the elements. – Felix Kling Feb 10 '11 at 10:15
Technically yes. Odds are there is one out in the wild already if you're willing to look and test it out for yourself. – xzyfer Feb 10 '11 at 10:17
Found a similar function on the [documentation](http://www.php.net/manual/en/function.array-diff.php#94596)... If only I thought to check again the documentation, instead of foolishly thinking it would compare all kind of elements after all the time I used it on one-dimensional arrays. There is a lesson to be learned here. – Eldros Feb 10 '11 at 10:30

score 3 · Answer 2 · answered Feb 10 '11 at 10:06

3

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]);

answered Feb 10 '11 at 10:06

xzyfer

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score 1 · Answer 3 · answered Feb 10 '11 at 10:07

1

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]);."

answered Feb 10 '11 at 10:07

Matt Gibson

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score 0 · Answer 4 · edited May 23 '17 at 11:52

0

Asked and answered here:

recursive array_diff()?

edited May 23 '17 at 11:52

Community

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answered Feb 10 '11 at 10:13

DhruvPathak

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Why does array_diff on arrays of arrays return an empty array?

4 Answers4

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