note 81815 modified in function.usort by thiago
| From: | thiago@php.net | Date: | Tue, 22 Jul 2008 19:09:52 +0000 |
| Subject: | note 81815 modified in function.usort by thiago | ||
| References: | 1 | Groups: | php.notes |
| Request: | Send a blank email to php-notes+get-142554@lists.php.net to get a copy of this message | ||
From the docs the user defined function looks as it could be arbitrary. This is not the case.
I needed a comparison that would send arbitrary values at the end of the array. Say '0'
means invalid for example.
So here is a sample function.
<?php
function array_cmp($a, $b) {
if( $a == 0 ) {
return 99;
} elseif( $a > $b ) {
return 1;
} elseif( $a == $b ) {
return 0;
} elseif( $a < $b ) {
return -1;
}
}
usort($test_array, "array_cmp");
print '<pre>'; print_r( $test_array ); print '</pre>';
$test_array = array(
'a' => 8 ,
'b' => 0 ,
'c' => 1 ,
'd' => 0 ,
'e' => 3
);
Output:
Array
(
[0] => 0
[1] => 1
[2] => 8
[3] => 0
[4] => 3
)
?>
This is beacause comparisons aren't applied to all possible pairs. So when the '0' is
tested as $b strange things can occur...
This is solved simply adding an
} elseif( $b == 0) {
return -99;
}
statement.
Carefull of the pitfalls. If you alter the ordering in strange ways without knowledge in the
underlying algorithm one could even trigger infinite loops. (if your testing for $a and $b for the
same value give inconsistent results. )
--was--
From the docs the user defined function looks as it could be arbitrary. This is not the case.
I needed a comparison that would send arbitrary values at the end of the array. Say '0'
means invalid for example.
So here is a sample function.
function array_cmp($a, $b) {
if( $a == 0 ) {
return 99;
} elseif( $a > $b ) {
return 1;
} elseif( $a == $b ) {
return 0;
} elseif( $a < $b ) {
return -1;
}
}
usort($test_array, "array_cmp");
print '<pre>'; print_r( $test_array ); print '</pre>';
$test_array = array(
'a' => 8 ,
'b' => 0 ,
'c' => 1 ,
'd' => 0 ,
'e' => 3
);
Output:
Array
(
[0] => 0
[1] => 1
[2] => 8
[3] => 0
[4] => 3
)
This is beacause comparisons aren't applied to all possible pairs. So when the '0' is
tested as $b strange things can occur...
This is solved simply adding an
} elseif( $b == 0) {
return -99;
}
statement.
Carefull of the pitfalls. If you alter the ordering in strange ways without knowledge in the
underlying algorithm one could even trigger infinite loops. (if your testing for $a and $b for the
same value give inconsistent results. )
http://php.net/manual/en/function.usort.php