Doc #80346 [Com]: Function `array_intersect_ukey`requires consistent comparison function

Edit report at https://bugs.php.net/bug.php?id=80346&edit=1 ID: 80346 Comment by: gilperon at gmail dot com Reported by: gilperon at gmail dot com Summary: Function array_intersect_ukeyrequires consistent comparison function Status: Open Type: Documentation Problem Package: Arrays related Operating System: ALL PHP Version: 7.4.12 Block user comment: N Private report: N New Comment: Thank you guys, but I think that most users will assume that the callback function will only be called when the comparson between the keys are effectively being done. I think most people will never assume that the callback will be called during the "sort" phase, which by the way, there is no single line saying that array_intersect (or similars) will sort the arrays previously. Also, I am running a very CPU intensive algorithm and I am trying to optimize every bit and because of the way my algorithm works, it already sorts the data before calling array_intersect. So is there a way to tell PHP not to sort the arrays and leave them untouched and just do the intersect, as it should? I think that it's not obvious to users to know that array_intersect (or similars) will sort the arrays before actually doing what it's meant to do. If so, it should be called array_sort_intersect or at least allow a FLAG to be set if the user already sorted the arrays by himself. Anyway, is there a way to me to check, inside the callback function, if the keys being compared are in the "sort" phase or in the "intersect" phase? Previous Comments: ------------------------------------------------------------------------ [2020-11-10 01:57:36] requinix@php.net Indeed, this is user error: as with every other array sorting function (and the intersect/diff functions *do* perform sorting - for efficiency), the callback needs to be consistent in its comparisons. It must return less than/equal to/greater than, and doing something else will likely result in "garbage in, garbage out" behavior. This matter is going to be common to all sorting, intersection, diff, etc. functions. If the docs are amended then I suggest some &copypasta; for each affected page. PS: Returning $key2 - $key1 is technically backwards, but the final sort order doesn't really matter since this function only cares about equality between elements. ------------------------------------------------------------------------ [2020-11-10 01:32:41] danack@php.net Changing the code: echo "DIFFERENT\n"; return 1; to: echo "DIFFERENT\n"; return $key2 - $key1; Makes your code work. It looks like this code may be sorting the arrays first, and sorting algorithms need to be stable: https://www.geeksforgeeks.org/stability-in-sorting-algorithms/ That's an educated guess. If it is that, it's a docs problem as stability probably should be mentioned. ------------------------------------------------------------------------ [2020-11-10 01:21:38] gilperon at gmail dot com Description: ------------ Run the test script. It has 2 arrays in such a way that only the key 4 appears on both. Using array_intersect_ukey does not return 4, instead it returns array(0) {}. Using array_intersect_key works perfectly. I also realized there is a bug in the implementation of this function, because if you run the test script it will show you this: |4|6|DIFFERENT |8|6|DIFFERENT |4|8|DIFFERENT |3|4|DIFFERENT |5|4|DIFFERENT |3|5|DIFFERENT |6|4|DIFFERENT |6|5|DIFFERENT |6|3|DIFFERENT It shouldnt be comparing 8 with 6 because these keys only appear on the 1st array and these keys shouldnt be compared at all. You can clearly see that this function, instead of comparing each key of the first array with each key of the second array, it's comparing the keys from the first array WITH ITSELF and then comparing the keys of the second array ITSELF (line |3|5|) and only then comparing the keys of both arrays together (but for some reason it misses the |4|4|). I know that in my simple use case I should be using array_intersect_key but I really need array_intersect_ukey to work properly because I have a much more complex use case for it. Test script: --------------- <?php $array1 = array(4 => true, 6 => true, 8 => true); $array2 = array(3 => true, 4 => true, 5 => true); var_dump(array_intersect_ukey( $array1, $array2, function ($key1, $key2) { echo "|" . $key1 . "|" . $key2 . "|"; if ($key1 === $key2) { echo "EQUAL\n"; return 0; } else{ echo "DIFFERENT\n"; return 1; } } )); ?> Expected result: ---------------- It should only show the element 4, which is present in both arrays. Actual result: -------------- Nothing is returned from the intersection. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=80346&edit=1