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

usort($unsortedObjectArray,'cmp');

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

Answer 2

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 3

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;
    }
}

Answer 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

Answer 5

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 6

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

Answer 7

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 8

I couldn't make the custom sort thing work with the above stated syntaxes, so if you receive complains about invalid sort function, try the following syntax for the sort operation itself (given that you have implemented a compare function "cmp":

usort($unsortedObjectsArray, array("myClassName", "cmp"));