PHP sorting object array by certain criteria? - php

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.