Sorting an Array of Objects in PHP In a Specific Order

Question

I have two arrays in PHP. The first array ($author_array) is comprised of user_ids in a particular order, like so: (8, 1, 6)

The second array ($user_results) is comprised of an array of objects like so:

Array
(
    [0] => stdClass Object
        (
            [ID] => 1
            [user_login] => user1
        )
    [1] => stdClass Object
        (
            [ID] => 6
            [user_login] => user6
        )
    [2] => stdClass Object
        (
            [ID] => 8
            [user_login] => user8
        )
)

I'd like to "sort" the second array so it's in this order, which matches the order of the values in the first array of (8, 1, 6). So it'd look like this:

Array
(
    [0] => stdClass Object
        (
            [ID] => 8
            [user_login] => user8
        )
    [1] => stdClass Object
        (
            [ID] => 1
            [user_login] => user1
        )
    [2] => stdClass Object
        (
            [ID] => 6
            [user_login] => user6
        )
)

I'm weak on data structures. How could I do this? :-)

Thanks in advance for your help!

-Bob

Paul Dixon · Accepted Answer · 2008-12-10 11:06:47Z

30

Use usort and provide a custom comparison function which uses the position of the key in your "ordering" array to determine the sort order, e.g. something like:

function cmp($a, $b) 
{
   global $author_array;

   $pos1=array_search ($a->ID, $author_array);
   $pos2=array_search ($b->ID, $author_array);

   if ($pos1==$pos2)
       return 0;
   else
      return ($pos1 < $pos2 ? -1 : 1);

}


usort($user_results, "cmp");

edited Dec 10, 2008 at 11:06

answered Dec 10, 2008 at 10:06

Paul Dixon

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4 Comments

Paul Dixon Over a year ago

Why the -1? It demonstrates a valid technique the OP might not have been aware of, and it different to the other answers as it performs the sort "in place" rather than making a copy of the original array.

gnud Over a year ago

Yes, who in their right mind downvotes a usort() solution when the issue is custom ordering? :| +1

Jacco Over a year ago

This is the solution that the PHP language developers recommend.

bobbyh Over a year ago

This worked beautifully when dropped into my code. I will now endeavor to understand how the heck it works! :-)

Tom Haigh · Accepted Answer · 2008-12-10 10:11:57Z

3

I'm not sure whether this will be significantly slower than other examples, but it seems simpler. It may be that you could build the $user_results array as an associative one to start with, using ID as the key, then you can easily do lookups.

$hash = array();
$result = array();

foreach ($user_results as $obj) {
    $hash[$obj->ID] = $obj;
}

foreach ($author_array as $id) {
    $result[] = $hash[$id];
}

answered Dec 10, 2008 at 10:11

Tom Haigh

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Comments

David · Accepted Answer · 2011-02-26 22:09:27Z

So I had a similar issue, but I was trying to order an object by an array (that wasn't an object). It's just not possible, so here's my workaround:

$sort_array= array(11, 4, 16, 19, 23);
$myobject = sort_categories($myobject)

function cmp($a, $b) { 
    if ($a->sort_key == $b->sort_key) { return 0; }
    return ($a->sort_key < $b->sort_key) ? -1 : 1;
}
function sort_categories($obj) {
    global $sort_array;

    foreach($obj as $cat) {
        $cat->sort_key = 999;
        for ($i=0;$i<count($sort_array);$i++) {
            if ($sort_array[$i] == $cat->term_id) $cat->sort_key = $i;
        }
    }
    usort($obj,'cmp');
    return $obj;
}

I'm looking through the object and adding a new (property?) called "sort_key" which we'll then use to sort on with usort() and cmp(). By default, the new sort_key will be 999 so it gets stuck at the end.

Emil · Accepted Answer · 2012-10-27 18:25:53Z

0

public static function reorganizeBykey ($objects, array $keys){
    $results = array();
    foreach($keys as $key){
        $i=0;
        foreach($objects as $object){
            if($object->sourceName==$key){
                $results[$i] = $object;
            }
            $i++;
        }
    }
    $others = (array_diff_assoc($objects,$results));
    $results = array_merge($results,$others);
    return $results;
}

I hope this is helpful – I had to use this to sort an array() by some keys() and then append what doesn't match at the end.

edited Oct 27, 2012 at 18:25

Emil

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answered Apr 20, 2012 at 22:15

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