two php arrays - sort one array with the value order of another [duplicate]

Question

I have two PHP arrays like so:

Array of X records containing the ID of Wordpress posts (in a particular order)
Array of Wordpress posts

The two arrays look something like this:

Array One (Sorted Custom Array of Wordpress Post IDs)

Array (  
  [0] => 54
  [1] => 10
  [2] => 4
)

Array Two (Wordpress Post Array)

Array ( 
    [0] => stdClass Object
        (
            [ID] => 4
            [post_author] => 1
    )
    [1] => stdClass Object
        (
            [ID] => 54
            [post_author] => 1
    )
    [2] => stdClass Object
        (
            [ID] => 10
            [post_author] => 1
    )
)

I would like to sort the array of wordpress posts with the order of the ID's in the first array.

edit: The server is running PHP Version 5.2.14

lonesomeday · Accepted Answer · 2011-01-09 23:05:04Z

10

This should be quite easy using usort, which sorts the array using a user-defined comparison function. The result might look something like this:

usort($posts, function($a, $b) use ($post_ids) {
    return array_search($a->ID, $post_ids) - array_search($b->ID, $post_ids);
});

Note that this solution, since it uses anonymous functions and closures, requires PHP 5.3.

One easy solution for this pre-5.3 (the dark ages!) is to do this with a quick loop and then ksort:

$ret = array();
$post_ids = array_flip($post_ids);
foreach ($posts as $post) {
    $ret[$post_ids[$post->ID]] = $post;
}
ksort($ret);

edited Jan 9, 2011 at 23:05

answered Jan 9, 2011 at 22:35

lonesomeday

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9 Comments

Richard Tuin Over a year ago

I was typing this exact same solution, +1. PS: i think you need to array_flip $post_ids before and after this function.

lonesomeday Over a year ago

@Richard Tuin That would be one solution -- the other is to use array_search, as I was in the middle of correcting my post to use.

Tisch Over a year ago

This looks like a very elegant solution, however, when I try and implement this, I'm getting confused to what the function is supposed to do? If I copy it straight from here I get : Parse error: syntax error, unexpected T_FUNCTION ---- I feel like I should be creating a function to do the comparison? (excuse the misunderstanding as well... I'm no doubt having a retard moment)... edit: reading this php.net/manual/en/function.usort.php seems to make it a little clearer, but still stuck!

lonesomeday Over a year ago

@Tisch $posts is your array of post objects; $post_ids is your array of ID values. To understand usort, it's probably easiest to read the manual page that I've linked to in my answer. If you are still uncertain, perhaps you could clarify what you're unsure about? This solution requires you have PHP 5.3 -- I'll edit my answer to reflect this.

goat Over a year ago

You could use array_flip() instead of array_search for the pre 5.3 solution, which would be much better for sorting a large list

|

jondavidjohn · Accepted Answer · 2011-01-09 22:32:07Z

2

You could create a nested looping mechanism to match up the order and ids and rebuild a new post array.

$new_post_array = array();

foreach($id_array as $id) {          //loop through custom ordered ids

    foreach($post_array as $post) {  //for every id loop through posts

        if($id == $post->ID){         //and when the custom ordered id matches the post->ID

            new_array[] = $post       //push the post on the new array

        }

    }

}

answered Jan 9, 2011 at 22:32

jondavidjohn

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3 Comments

Richard Tuin Over a year ago

Making a copy of both the arrays (that's what foreach does) is unneccesary here.

Tisch Over a year ago

Thankyou for your answer. This does the job, however seems a little sluggish? I've accepted the answer anyway because it does do what I am looking for, and works with PHP 5.2

Tisch Over a year ago

sorry @jondavidjohn, I've had to switch to the faster solution. Thanks again.

goat · Accepted Answer · 2011-01-09 22:35:44Z

2

$sortOrderMap = array_flip($postIds);

usort($posts, function($postA, $postB) use ($sortOrderMap) {
    return $sortOrderMap[$postA->ID] - $sortOrderMap[$postB->ID];
});

You can simply subtract b from a instead of a from b to sort the other direction

answered Jan 9, 2011 at 22:35

goat

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1 Comment

Tisch Over a year ago

thankyou for your answer as well... The solution above is very similar so I'm going to pursue that one if possible. Looks like PHP 5.2 is stopping me though :(

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