Doc #81692 [Com]: array_unique bug

Edit report at https://bugs.php.net/bug.php?id=81692&edit=1 ID: 81692 Comment by: stanislav dot eismont at gmail dot com Reported by: stanislav dot eismont at gmail dot com Summary: array_unique bug Status: Verified Type: Documentation Problem Package: Arrays related Operating System: ubuntu 20.04 PHP Version: 7.4.26 Block user comment: N Private report: N New Comment: To me it isn't look like a doc related problem. I gave such a big array as an example for a reason. If you change this array somehow, let's say remove last element, then there will be one "red" value printed https://3v4l.org/tpjMt. Previous Comments: ------------------------------------------------------------------------ [2021-12-03 15:30:54] cmb@php.net > Isn't this just a result of inconsistent comparisons during > sorting? Right, although PHP 5 produced the required results[1]. Anyhow, SORT_REGULAR has a fundamental flaw when working on arbitrarly mixed scalar types, namely that the result is not necessarily in monotonic order, i.e. the sort has arbitrary results (depending on the sorting algorithm). E.g. consider ['2', 'a', 1]; the following holds prior to PHP 8.0.0: '2' < 'a' 'a' < 1 '2' > 1 As of PHP 8.0.0, this is no longer the case for the given example (thanks to the saner string to number comparisons), but consider another example: ['!', '0', true]; the following holds: '!' < '0' '0' < true '!' == true That still doesn't work. So the current O(log n) algorithm of array_unique(), would need to be changed to an O(n²) algorithm, or the sorting algorithm would need to be changed back to what we had in PHP 5. Neither option is desireable, and I think we should just document this limitation. (And we also should fix the note in the description section, which only applies for SORT_STRING.) [1] <https://3v4l.org/RfFJr> ------------------------------------------------------------------------ [2021-12-03 15:13:58] requinix@php.net Isn't this just a result of inconsistent comparisons during sorting? The sorted arrays don't place the two reds next to each other with SORT_REGULAR; they do if you use SORT_STRING, which also produces the expected unique array. https://3v4l.org/JTQMr https://3v4l.org/gPaPn ------------------------------------------------------------------------ [2021-12-03 12:25:04] cmb@php.net Indeed, broken as of PHP 7.0.0: <https://3v4l.org/PXQZe>. ------------------------------------------------------------------------ [2021-12-03 11:30:02] stanislav dot eismont at gmail dot com Description: ------------ array_unique returns incorrect result with SORT_REGULAR flag. Test script: --------------- <?php $array = ["red", "color" => "red", 78, 78, 12, "12", false, null, false, 0, true, 1, 0, null, 2.12, "2.12", 8, "-s"]; var_dump(array_unique($array, SORT_REGULAR)); Expected result: ---------------- Expected one "red" value printed: array(11) { [0]=> string(3) "red" // ... } Actual result: -------------- Actually "red" printed twice: array(11) { [0]=> string(3) "red" ["color"]=> string(3) "red" // ... } ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=81692&edit=1