(PHP 3>= 3.0.3, PHP 4 >= 4.0.0)
usort --
Sort an array by values using a user-defined comparison function
Description
void
usort ( array array, string cmp_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.
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. If two members compare as equal, their order in the
sorted array is undefined.
Example 1. usort() example function cmp ($a, $b) {
if ($a == $b) return 0;
return ($a > $b) ? -1 : 1;
}
$a = array (3, 2, 5, 6, 1);
usort ($a, "cmp");
while (list ($key, $value) = each ($a)) {
echo "$key: $value\n";
} |
|
This example would display:
Note:
Obviously in this trivial case the rsort()
function would be more appropriate.
Example 2.
usort() example using multi-dimensional array
function cmp ($a, $b) {
return strcmp($a["fruit"], $b["fruit"]);
}
$fruits[0]["fruit"] = "lemons";
$fruits[1]["fruit"] = "apples";
$fruits[2]["fruit"] = "grapes";
usort($fruits, "cmp");
while (list ($key, $value) = each ($fruits)) {
echo "\$fruits[$key]: " . $value["fruit"] . "\n";
} |
|
When sorting a multi-dimensional array, $a and $b contain
references to the first index of the array.
This example would display:
$fruits[0]: apples
$fruits[1]: grapes
$fruits[2]: lemons |
Note: Instead of a function name, an
array containing an object reference and a method name can also be
supplied.
Example 3.
usort() example using a member function of an object
class TestObj {
var $name;
function TestObj($name)
{
$this->name = $name;
}
/* This is the static comparing function: */
function cmp_obj($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");
$a[] = new TestObj("d");
uasort($a, array ("TestObj", "cmp_obj"));
foreach ($a as $item) {
print $item->name."\n";
} |
|
This example would display:
| Warning |
The underlying quicksort function in some C libraries (such as
on Solaris systems) may cause PHP to crash if the comparison
function does not return consistent values.
|
See also uasort(),
uksort(), sort(),
asort(),
arsort(),ksort(),
natsort(), and rsort().
