Sort arrays into multidimensional array by key

Question

I have a database table which gives me the following result:

array(8) {
    ["link_id"]=>
    string(2) "20"
    ["link_url"]=>
    string(56) "http://url.of/website"
    ["link_name"]=>
    string(34) "Website title"
    ["link_target"]=>
    string(0) ""
    ["link_description"]=>
    string(0) ""
    ["link_updated"]=>
    string(19) "2009-05-24 16:51:04"
    ["taxonomy_id"]=>
    string(2) "36"
    ["term_id"]=>
    string(2) "34"
    ["category_name"]=>
    string(15) "Link category"
}

I want to sort many of these arrays in to one multidimensional array, based on the category_name key, and then sorted by the link_updated key.

So I eventually want it to look like this:

array(2) {
    ["First category"]=>
    array(2) {
        ["link_name"]=>
        string(11) "Newest link"
        ["link_updated"]=>
        string(19) "2009-05-24 16:51:24"
    }
    ["Second category"]=>
    array(2) {
        ["link_name"]=>
        string(10) "Older link"
        ["link_updated"]=>
        string(19) "2009-05-20 05:32:56"
    }
}

I have no idea how to do this, but I think I have to make my own sorting method (usort())?

EDIT: I want to show 5 links in each category.

Answer 1

array_multisort should do the trick here - it's quite powerful.

Answer 2

Using usort() you can sort your arrays in any way you want:

function sort_crazy_way($a, $b){
  // do your business.
}

usort($array, 'sort_crazy_way');

After you get it sorted, you can create the last array in another for loop.

From the PHP manual:

The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

So, your comparison function should be something like:

function sort_crazy_way($a, $b){
  $sorted_by_category = strcmp($a['category_name'], $b['category_name']);
  if($sorted_by_category){
    return $sorted_by_category;
  }

  // If we're here, category_name is the same. Compare link_updated.

  $time_diff = strtotime($a['link_updated']) - strtotime($b['link_updated']);
  return $time_diff;
}

Answer 3

I solved it myself, by using the following code:

foreach ($bookmarks as $b)
{
    $category[$b["category_name"]][] = array(
        "link_id" => $b["link_id"],
        "link_url" => $b["link_url"],
        "link_name" => $b["link_name"],
        "link_target" => $b["link_target"],
        "link_description" => $b["link_description"],
        "link_updated" => $b["link_updated"],
        "taxonomy_id" => $b["taxonomy_id"],
        "term_id" => $b["term_id"],
        "category_name" => $b["category_name"]
    );
}

This creates an array of the category name, and puts all subarrays in the right parent array (based on category). The sorting after time the link is updated is being made in the SQL query.