usort
Sort an array by values using a user-defined comparison function
&reftitle.description;
trueusort
arrayarray
callablecallback
Sorts array in place by values using a
user-supplied comparison function to determine the order.
¬e.sort-unstable;
¬e.no-key-association;
&reftitle.parameters;
array
The input array.
callback
&sort.callback.description;
&reftitle.returnvalues;
&return.true.always;
&reftitle.changelog;
&Version;
&Description;
&return.type.true;
&array.changelog.by-ref;
&reftitle.examples;
<function>usort</function> example
$value) {
echo "$key: $value\n";
}
?>
]]>
&example.outputs;
The spaceship operator may be used to
simplify the internal comparison even further.
$b;
}
$a = array(3, 2, 5, 6, 1);
usort($a, "cmp");
foreach ($a as $key => $value) {
echo "$key: $value\n";
}
?>
]]>
Obviously in this trivial case the sort
function would be more appropriate.
<function>usort</function> example using multi-dimensional array
$value) {
echo "\$fruits[$key]: " . $value["fruit"] . "\n";
}
?>
]]>
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, $b)
{
return strtolower($a->name) <=> strtolower($b->name);
}
}
$a[] = new TestObj("c");
$a[] = new TestObj("b");
$a[] = new TestObj("d");
usort($a, [TestObj::class, "cmp_obj"]);
foreach ($a as $item) {
echo $item->name . "\n";
}
?>
]]>
&example.outputs;
<function>usort</function> example using a <link linkend="functions.anonymous">closure</link>
to sort a multi-dimensional array
'z', 'key_b' => 'c');
$array[1] = array('key_a' => 'x', 'key_b' => 'b');
$array[2] = array('key_a' => 'y', 'key_b' => 'a');
function build_sorter($key) {
return function ($a, $b) use ($key) {
return strnatcmp($a[$key], $b[$key]);
};
}
usort($array, build_sorter('key_b'));
foreach ($array as $item) {
echo $item['key_a'] . ', ' . $item['key_b'] . "\n";
}
?>
]]>
&example.outputs;
<function>usort</function> example using the spaceship operator
The spaceship operator allows for straightforward comparison of
compound values across multiple axes. The following example will sort
$people by last name, then by first name if the
last name matches.
'Adam', 'last' => 'West'];
$people[1] = ['first' => 'Alec', 'last' => 'Baldwin'];
$people[2] = ['first' => 'Adam', 'last' => 'Baldwin'];
function sorter(array $a, array $b) {
return [$a['last'], $a['first']] <=> [$b['last'], $b['first']];
}
usort($people, 'sorter');
foreach ($people as $person) {
print $person['last'] . ', ' . $person['first'] . PHP_EOL;
}
?>
]]>
&example.outputs;
&reftitle.seealso;
uasort
uksort
&seealso.array.sorting;