How to sort a PHP array based on a second array?

Question

I have two simple arrays. One is an array of posts ($posts) and the other is an array of post ID's that should be on top of the stream, like they are featured ($featured). I am trying to find an efficient way to loop through them and if an ID is in both arrays, move it to the beginning of the $posts array, and the ones that are moved should be sorted ASC by $featured['order'], so for example, some posts ($posts):

Array
(
 [ab77] => Status_Update Object
 (
 [id] => ab77
 [title] => Status Update
 )
 [b4k7] => Status_Update Object
 (
 [id] => b4k7
 [title] => Status Update
 )
 [4d55] => Status_Update Object
 (
 [id] => 4d55
 [title] => Status Update
 )
 [13c5] => Status_Update Object
 (
 [id] => 13c5
 [title] => Status Update
 )
 [3aa2] => Status_Update Object
 (
 [id] => 3aa2
 [title] => Status Update
 )
)

and then some posts which should be featured ($featured):

Array
(
 [13c5] => Array
 (
 [id] => 13c5
 [order] => 1
 )
 [3a71] => Array
 (
 [id] => 3a71
 [order] => 2
 )
 [4d55] => Array
 (
 [id] => 4d55
 [order] => 3
 )
)

So the $posts array should end up sorted like this:

13c5 4d55 ab77 bk47 3aa2

How do I do this without a bunch of slow loops?

• scrowler: It looks like you've got the ID as the array keys already, so you won't need nested loops - just one and inside you can check array_key_exists('13c5', $featured)) etc
• DutGRIFF: If possible I would build the arrays out correctly in the first place. This will most likely be faster and elegant. It sounds like you want to create a new array of data from two existing queries. My suggestion is make a new query that give you the data you want instead of manipulating the existing data. This may not be best for your situation but in many cases it is.
• Barmar: Use uksort to sort using a user-written comparison function. The function should check whether both keys are in the featured array using array_key_exists. If they're both in or both not in, compare them with <.
• 0pc0d3: how do i do that and then also sort the ones that get moved, by their order key?
• 0pc0d3: DutGRIFF unfortunately, the arrays are coming from to separate databases entirely, so i cannot join.

Answer 1

This should be doable with uksort() and closures:

uksort( $posts, function ( $a, $b ) use ( $featured ) {
 $fa = ( isset( $featured[$a] ) ? $featured[$a]['order'] : INF );
 $fb = ( isset( $featured[$b] ) ? $featured[$b]['order'] : INF );
 if ( $fa != $fb ) return ( $fa < $fb ? -1 : +1 );
 // could add a tie-breaker comparison here
 return 0;
} );

• 0pc0d3: That almost works, it returns the not-featured posts on top with the featured ones on the bottom but sorted correctly, like this: ab77 bk47 3aa2 13c5 4d55
• 0pc0d3: I'm trying to get to 13c5 4d55 ab77 bk47 3aa2
• Ilmari Karonen: Strange. Can you show the exact code you're using? And maybe use var_dump() instead of print_r() to display the arrays, so that there's no ambiguity about types?

Answer 2

This is the messy answer I came up with works.

$found, $not_found = array();
foreach ($posts as $key => $value) {
 if (array_key_exists($key, $featured)) {
 $found[$key] = $value;
 } else {
 $not_found[$key] = $value;
 }
}
usort($found, 'sort_by_order');
function sort_by_order ($a, $b) {
 return $a['order'] - $b['order'];
}
$new = array_merge($found, $not_found);