Edit report at https://bugs.php.net/bug.php?id=81692&edit=1
ID: 81692
Updated by: cmb@php.net
Reported by: stanislav dot eismont at gmail dot com
Summary: array_unique bug
Status: Verified
-Type: Bug
+Type: Documentation Problem
Package: Arrays related
Operating System: ubuntu 20.04
PHP Version: 7.4.26
-Assigned To: cmb
+Assigned To:
Block user comment: N
Private report: N
New Comment:
> 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>
Previous Comments:
------------------------------------------------------------------------
[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"
// ...
}
------------------------------------------------------------------------
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Edit this bug report at https://bugs.php.net/bug.php?id=81692&edit=1