usort
Sort an array by values using a user-defined comparison function
Description
boolusort
array&array
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.
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.
Up to PHP 4.0.6 the user defined functions would keep the original order for
those elements, but with the new sort algorithm introduced with 4.1.0 this
is no longer the case as there is no solution to do so in an efficient way.
&return.success;
<function>usort</function> example
]]>
This example would display:
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.
This example would display:
<function>usort</function> example using a member function of an object
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");
$a[] = new TestObj("d");
usort($a, array("TestObj", "cmp_obj"));
foreach ($a as $item) {
echo $item->name . "\n";
}
?>
]]>
This example would display:
See also uasort,
uksort, sort,
asort,
arsort,ksort,
natsort, and rsort.