Question

I have an array of objects which I want to sort based on one property, and then kind of ‘group together’ based on another property. In the example below, I would like them sorted based on $sequence, and grouped based on $artist.

// a stripped down version of my class :

<?php
class myClass
{
    public $sequence;
    public $artist;

    function __construct($sequence,$artist)
    {
        $this->sequence=$sequence;
        $this->artist=$artist;
    }

    static function cmp_myclass_sequence($a, $b)
    {
        $a_seq = $a->sequence;
        $b_seq = $b->sequence;
        if ($a_seq == $b_seq) {
            return 0;
        }
        return ($a_seq > $b_seq) ? +1 : -1;
    }
    static function cmp_myclass_artist($a, $b)
    {
        $a_art = strtolower($a->artist);
        $b_art = strtolower($b->artist);
        if ($a_art == $b_art) {
            return 0;
        }
        return ($a_art > $b_art) ? +1 : -1;
    }
}

//some objects of my class which am using for testing :

$myObj1 = new myClass(1,'A');
$myObj2 = new myClass(1,'B');
$myObj3 = new myClass(1,'C');
$myObj4 = new myClass(2,'A');
$myObj5 = new myClass(2,'B');
$myObj6 = new myClass(2,'C');
$myObj7 = new myClass(4,'A');
$myObj8 = new myClass(5,'A');
$myObj9 = new myClass(3,'B');
$myObj10 = new myClass(3,'G');
$myObj11= new myClass(3,'A');

$myArr=array($myObj1,$myObj2,$myObj3,$myObj4,$myObj5,$myObj6,$myObj7,$myObj8,$myObj9,$myObj10,$myObj11);

echo "My Array Before sort : <br>";
foreach ($myArr as $obj){ print_r($obj); echo "<br>"; }

usort($myArr, array("myClass", "cmp_myclass_sequence"));
//usort($myArr, array("myClass", "cmp_myclass_artist"));


echo "My Array AFTER sort : <br>";
foreach ($myArr as $obj){ print_r($obj); echo "<br>";}

?>

Both the sorting functions that I have in the class, cmp_myclass_sequence and cmp_myclass_artist work well on their own. But I am not sure how to get the array grouped in this way :
All the A artists come first, then the B and so on.
Amongst the A artists, the objects should be sorted by the sequence int of that object.

In short this is the result that am looking for :

/*
My Array AFTER sort : 

myClass Object ( [sequence] => 1 [artist] => A )
myClass Object ( [sequence] => 2 [artist] => A )
myClass Object ( [sequence] => 3 [artist] => A )
myClass Object ( [sequence] => 4 [artist] => A )
myClass Object ( [sequence] => 5 [artist] => A )
myClass Object ( [sequence] => 1 [artist] => B )
myClass Object ( [sequence] => 2 [artist] => B )
myClass Object ( [sequence] => 3 [artist] => B )
myClass Object ( [sequence] => 1 [artist] => C )
myClass Object ( [sequence] => 2 [artist] => C )
myClass Object ( [sequence] => 3 [artist] => G ) 
*/

Answer 1

You can do this easily with one compare function:

function sort_c_arr($item_1, $item_2)
{
   if($item_1->artist != $item_2->artist)
   {
      return strcmp($item_1->artist, $item_2->artist);
   }
   return $item_1->sequence - $item_2->sequence;
}
// ...
usort($arr, 'sort_c_arr');