ID: 45988
User updated by: php at sameprecision dot org
Reported By: php at sameprecision dot org
-Status: Open
+Status: Bogus
Bug Type: Arrays related
Operating System: irrelevant
PHP Version: 5.2.6
New Comment:
I think I have made a mistake in trying to use a generalized sorting
algorithm with a comparison operation that is not transitive.
The operation HAS to be transitive or there will always be an example
that doesn't work.
sorry!
Previous Comments:
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[2008-09-03 20:38:01] php at sameprecision dot org
Description:
------------
Using usort, not all pairs of elements are compared. If a comparison
operation is not transitive, this leads to unexpected ordering, even
though every pair of elements are comparable.
This should probably be mentioned in the documentation.
Reproduce code:
---------------
//goal: sort $array so that an element is not a substring of any
subsequent elements
$array = array('aa','b','a');
//if $a is a substring of $b, return 1. Else return -1
function compare($a,$b){
return strpos($b,$a)===false ? -1 : 1;
}
usort($array,'compare');
print_r($array);
Expected result:
----------------
Array ( [0] => aa [1] => b [2] => a )
Actual result:
--------------
Array ( [0] => a [1] => b [2] => aa )
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Edit this bug report at http://bugs.php.net/?id=45988&edit=1
