usort
Sort an array by values using a user-defined comparison function
&reftitle.description;
boolusort
arrayarray
callbackcmp_function
This function will sort an array by its values using a user-supplied
comparison function. If the array you wish to sort needs to be sorted by
some non-trivial criteria, you should use this function.
If two members compare as equal, their order in the sorted array is undefined.
¬e.no-key-association;
&reftitle.parameters;
array
The input array.
cmp_function
The comparison function must return an integer less than, equal to, or
greater than zero if the first argument is considered to be
respectively less than, equal to, or greater than the second.
&reftitle.returnvalues;
&return.success;
&reftitle.changelog;
&Version;
&Description;
4.1.0
A new sort algorithm was introduced. The cmp_function
doesn't keep the original order for elements comparing as equal.
&reftitle.examples;
<function>usort</function> example
$value) {
echo "$key: $value\n";
}
?>
]]>
&example.outputs;
Obviously in this trivial case the sort
function would be more appropriate.
<function>usort</function> example using multi-dimensional array
]]>
When sorting a multi-dimensional array, $a and
$b contain references to the first index of the array.
&example.outputs;
<function>usort</function> example using a member function of an object
name = $name;
}
/* This is the static comparing function: */
static function cmp_obj($a, $b)
{
$al = strtolower($a->name);
$bl = strtolower($b->name);
if ($al == $bl) {
return 0;
}
return ($al > $bl) ? +1 : -1;
}
}
$a[] = new TestObj("c");
$a[] = new TestObj("b");
$a[] = new TestObj("d");
usort($a, array("TestObj", "cmp_obj"));
foreach ($a as $item) {
echo $item->name . "\n";
}
?>
]]>
&example.outputs;
&reftitle.seealso;
uasort
uksort
sort
asort
arsort
ksort
natsort
rsort