Bug #69866 [Opn->Nab]: usort call with same keys problem

Edit report at https://bugs.php.net/bug.php?id=69866&edit=1 ID: 69866 Updated by: requinix@php.net Reported by: dmifedorenko at gmail dot com Summary: usort call with same keys problem -Status: Open +Status: Not a bug Type: Bug Package: Arrays related Operating System: Linux vm 3.13.0-37-generic #64-U PHP Version: 7.0Git-2015-06-18 (Git) Block user comment: N Private report: N New Comment: usort() does not produce stable results if the comparison function is inconsistent. Your function claims that both items in $result should sort after the other so you'll get different results with different initial orders. If you make your function behave properly then not only will you get the "right" result but you'll get it in every version of PHP. For example, you could do return $b[1] - $a[1]; Note that sorting this way will claim both items are equal and, just like what happens with an inconsistent comparison function, their sort order will be undefined and thus vary with the initial ordering. Obviously if you took both numbers into consideration then that wouldn't happen: return ($b[1] - $a[1]) ?: ($b[0] - $a[0]); Previous Comments: ------------------------------------------------------------------------ [2015-06-18 03:45:40] dmifedorenko at gmail dot com Description: ------------ Different usort behavior in php5.6 and php7. 5.6 returns first array element, and 7 returns last element. Test script: --------------- $results = array( array(2001, 1), array(2002, 1), ); usort($results, function ($a, $b) { return $a[1] > $b[1] ? -1 : 1; }); var_dump($results[0][0]); Expected result: ---------------- int(2001) Actual result: -------------- int(2002) ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=69866&edit=1