Sort Object in PHP

Almost verbatim from the manual:

function compare_weights($a, $b) { 
    if($a->weight == $b->weight) {
        return 0;
    } 
    return ($a->weight < $b->weight) ? -1 : 1;
} 

usort($unsortedObjectArray, 'compare_weights');

If you want objects to be able to sort themselves, see example 3 here: http://php.net/usort

You can even build the sorting behavior into the class you're sorting, if you want that level of control

class thingy
{
    public $prop1;
    public $prop2;

    static $sortKey;

    public function __construct( $prop1, $prop2 )
    {
        $this->prop1 = $prop1;
        $this->prop2 = $prop2;
    }

    public static function sorter( $a, $b )
    {
        return strcasecmp( $a->{self::$sortKey}, $b->{self::$sortKey} );
    }

    public static function sortByProp( &$collection, $prop )
    {
        self::$sortKey = $prop;
        usort( $collection, array( __CLASS__, 'sorter' ) );
    }

}

$thingies = array(
        new thingy( 'red', 'blue' )
    ,   new thingy( 'apple', 'orange' )
    ,   new thingy( 'black', 'white' )
    ,   new thingy( 'democrat', 'republican' )
);

print_r( $thingies );

thingy::sortByProp( $thingies, 'prop1' );

print_r( $thingies );

thingy::sortByProp( $thingies, 'prop2' );

print_r( $thingies );

For that compare function, you can just do:

function cmp( $a, $b )
{ 
    return $b->weight - $a->weight;
} 

The usort function (http://uk.php.net/manual/en/function.usort.php) is your friend. Something like...

function objectWeightSort($lhs, $rhs)
{
   if ($lhs->weight == $rhs->weight)
     return 0;

   if ($lhs->weight > $rhs->weight)
     return 1;

   return -1;
}

usort($unsortedObjectArray, "objectWeightSort");

Note that any array keys will be lost.

You could use the usort() function and make your own comparison function.

$sortedObjectArray = usort($unsortedObjectArray, 'sort_by_weight');

function sort_by_weight($a, $b) {
    if ($a->weight == $b->weight) {
        return 0;
    } else if ($a->weight < $b->weight) {
        return -1;
    } else {
        return 1;
    }
}

Depending on the problem you are trying to solve, you may also find the SPL interfaces useful. For example, implementing the ArrayAccess interface would allow you to access your class like an array. Also, implementing the SeekableIterator interface would let you loop through your object just like an array. This way you could sort your object just as if it were a simple array, having full control over the values it returns for a given key.

For more details:

• Zend Article
• PHPriot Article
• PHP Manual

Update from 2022 - sort array of objects:

usort($array, fn(object $a, object $b): int => $a->weight <=> $b->weight);

Full example:

$array = [
    (object) ['weight' =>  5],
    (object) ['weight' => 10],
    (object) ['weight' =>  1],
];

usort($array, fn(object $a, object $b): int => $a->weight <=> $b->weight);
// Now, $array is sorted by objects' weight.

// display example :
echo json_encode($array);

Output:

[{"weight":1},{"weight":5},{"weight":10}]

Documentation links:

• usort
• spaceship operator (PHP 7.0)
• scalar type declaration (PHP 7.0)
• return type declaration (PHP 7.0)
• arrow function (PHP 7.4)

If you want to explore the full (terrifying) extent of lambda style functions in PHP, see: http://docs.php.net/manual/en/function.create-function.php