Sort Object in PHP

Question

What is an elegant way to sort objects in PHP? I would love to accomplish something similar to this.

$sortedObjectArary = sort($unsortedObjectArray, $Object->weight);

Basically specify the array I want to sort as well as the field I want to sort on. I looked into multidimensional array sorting and there might be something useful there, but I don't see anything elegant or obvious.

Answer 1

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

Answer 2

For php >= 5.3

function osort(&$array, $prop)
{
    usort($array, function($a, $b) use ($prop) {
        return $a->$prop > $b->$prop ? 1 : -1;
    }); 
}

Note that this uses Anonymous functions / closures. Might find reviewing the php docs on that useful.

Answer 3

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 );

Answer 4

For that compare function, you can just do:

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

Answer 5

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.

Answer 6

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;
    }
}