PHP sorting object array by certain criteria?

Question

I have something like this:

$i = 0;

foreach($tracks['results'] as $track){
    $trackName[$i] = $track['name'];
    $trackPlaycount[$track['name']] = $track['playcount'];
    $trackPercent[$track['name']] = $track['percent'];
    $i++;
}

$this->trackName = $trackName;
$this->trackPlaycount = $trackPlaycount;
$this->trackPercent = $trackPercent;

how could I sort these objects by playcount? From what I have read so far I understand I should probably create a compare function and then make it work with usort(), right? But I'm not quite sure how to accomplish that...

thank you

edit: ok, so now I've got it like this:

public function firstmethod(){
    // there are some more parameters here of course
    // but they worked before, not important for the problem
    $i = 0;
    foreach($tracks['results'] as $track){
        $trackName[$i] = $track['name'];
        $trackPlaycount[$track['name']] = $track['playcount'];
        $trackPercent[$track['name']] = $track['percent'];
        // this part is new
        $tracksArray[$i] = array(
            'name' => $trackName[$i], 
            'playcount' => $trackPlaycount[$track['name']], 
            'percentage' => $trackPercent[$track['name']]
        );
        $i++;
    }

    usort($tracksArray, array($this, 'sortByCount'));

    $i = 0;
    // this is to put the new sorted array into the old variables? 
    foreach($tracksArray as $temp){
        $trackName[$i] = $temp['name'];
        $trackPlaycount[$trackName[$i]] = $temp['playcount'];
        $trackPercent[$trackName[$i]] = $temp['percentage'];
        $i++;
    }

    $this->trackName = $trackName;
    $this->trackPlaycount = $trackPlaycount;
    $this->trackPercent = $trackPercent;
}


public function sortByCount($a, $b){
    if($a["playcount"] == $b["playcount"]) {
        return 0;
    }
    return ($a["playcount"] < $b["playcount"]) ? -1 : 1;
}   

this now works... thank you everyone

Answer 1

usort example:

In the custom function you just access the array key you care about like this:

?php
$people = array(
    array('id' => 1, 'name' => 'John', 'age' => 12),
    array('id' => 2, 'name' => 'Mary', 'age' => 14),
    array('id' => 3, 'name' => 'Aaaaaadam', 'age' => 15)
);

usort($people, "sortByName");
var_dump($people);
usort($people, "sortByAge");
var_dump($people);

function sortByName($a, $b) {
    return strcmp($a["name"], $b["name"]);
}

function sortByAge($a, $b) { // or playcount or whatever
    if($a["age"] == $b["age"]) {
        return 0;
    }
    return ($a["age"] < $b["age"]) ? -1 : 1;
}

prints the sorted array (only pasted one so it's not getting to long, other output accordingly sorted by age)

array(3) {
  [0]=>
  array(3) {
    ["id"]=>
    int(3)
    ["name"]=>
    string(9) "Aaaaaadam"
    ["age"]=>
    int(15)
  }
  [1]=>
  array(3) {
    ["id"]=>
    int(1)
    ["name"]=>
    string(4) "John"
    ["age"]=>
    int(12)
  }
  [2]=>
  array(3) {
    ["id"]=>
    int(2)
    ["name"]=>
    string(4) "Mary"
    ["age"]=>
    int(14)
  }
}

Answer 2

You could also use an SplMaxHeap for this. Borrowing @edorian's $people array, you can do

class SortByAge extends SplMaxHeap
{
    function compare($a, $b)
    {
        return $a['age'] - $b['age'];
    }
}

$sort = new SortByAge;
foreach($people as $person) {
    $sort->insert($person);
}

print_r(iterator_to_array($sort));

This should perform somewhat better than usort.