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?

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 — scrowler
– scrowler, Commented Apr 27, 2015 at 21:51
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. — DutGRIFF
– DutGRIFF, Commented Apr 27, 2015 at 21:51
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 <. — Barmar
– Barmar, Commented Apr 27, 2015 at 21:52
how do i do that and then also sort the ones that get moved, by their order key? — 0pc0d3
– 0pc0d3, Commented Apr 27, 2015 at 21:52
DutGRIFF unfortunately, the arrays are coming from to separate databases entirely, so i cannot join. — 0pc0d3
– 0pc0d3, Commented Apr 27, 2015 at 21:53

Ilmari Karonen · Accepted Answer · 2015-04-27 21:59:17Z

3

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;
} );

answered Apr 27, 2015 at 21:59

Ilmari Karonen

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3 Comments

0pc0d3 Over a year ago

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 Over a year ago

I'm trying to get to 13c5 4d55 ab77 bk47 3aa2

Ilmari Karonen Over a year ago

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?

0pc0d3 · Accepted Answer · 2015-04-27 23:36:35Z

0

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);

answered Apr 27, 2015 at 23:36

0pc0d3

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