Question

2

1

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

edited Dec 10 at 11:04

Paul Dixon
16k●18●45

asked Dec 10 at 9:53

bobbyh
27●4

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Paul Dixon · Accepted Answer · 12/10/2008 11:06:47 AM UTC

8

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 at 11:06

answered Dec 10 at 10:06

Paul Dixon
16k●18●45

	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. – Paul Dixon Dec 10 at 11:13
	Yes, who in their right mind downvotes a usort() solution when the issue is custom ordering? :\| +1 – gnud Dec 10 at 11:16
	This is the solution that the PHP language developers recommend. – Jacco Dec 10 at 11:28
	This worked beautifully when dropped into my code. I will now endeavor to understand how the heck it works! :-) – bobbyh Dec 11 at 2:47

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tomhaigh · Answer 2 · 12/10/2008 10:11:57 AM UTC

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];
}

tomhaigh · Answer 3 · 12/10/2008 12:23:17 PM UTC

Paul Dixon's answer is better than my other one, but if you want to use it without having to use a global you could do something like this:

class sortTest {
    private $author_array;
    public function sort(&$user_results, $author_array) {
        $this->author_array = $author_array;
        usort($user_results, array($this, 'cmp'));
    }

    function cmp($a, $b) 
    {

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

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

$sorter = new sortTest();
$sorter->sort($user_results, $author_array);

Sorting an Array of Objects in PHP In a Specific Order

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