Rearrange get_categories array compared to another array

Question

I've got a function that pulls the latest post from each category and arrange categories by latests posts. What I get from this is an array with category ids which I want to use to rearrange the get_categories array.

/* Get all categories */
$categories = get_categories();
/* Create empty array */
$categories_order = [];
/* For each category */
foreach($categories as $category) {
  /* Modify WP query */
  $args = array('posts_per_page' => 1, /* Max 1 post */
                'category__in' => array($category->term_id), /* In this specific category */
                'ignore_sticky_posts' => true ); /* No sticky posts */
  /* Get all posts from categories with modifier */
  $posts = get_posts($args);
  /* If there are posts */
  if ($posts) {
    /* For each post */
    foreach($posts as $post) {
      /* Add to array key => value (category id => time published) */
      $categories_order[$category->term_id] = get_post_time('YmdHis');
    }
  }
}
arsort($categories_order); /* Order new array by value */
$categories_order = array_keys($categories_order); /* Remove array values */
print_r($categories_order);

My function returns:

Array ( [0] => 2 [1] => 5 [2] => 4 )

get_categories returns:

Array
(
    [1] => stdClass Object
        (
            [term_id] => 2
            [name] => Спорт
            [slug] => sport
            [term_group] => 0
            [term_taxonomy_id] => 2
            [taxonomy] => category
            [description] => 
            [parent] => 0
            [count] => 6
            [cat_ID] => 2
            [category_count] => 6
            [category_description] => 
            [cat_name] => Спорт
            [category_nicename] => sport
            [category_parent] => 0
        )

    [2] => stdClass Object
        (
            [term_id] => 4
            [name] => Дом и градина
            [slug] => home-and-garden
            [term_group] => 0
            [term_taxonomy_id] => 4
            [taxonomy] => category
            [description] => 
            [parent] => 0
            [count] => 1
            [cat_ID] => 4
            [category_count] => 1
            [category_description] => 
            [cat_name] => Дом и градина
            [category_nicename] => home-and-garden
            [category_parent] => 0
        )

    [3] => stdClass Object
        (
            [term_id] => 5
            [name] => Транспорт
            [slug] => transport
            [term_group] => 0
            [term_taxonomy_id] => 5
            [taxonomy] => category
            [description] => 
            [parent] => 0
            [count] => 1
            [cat_ID] => 5
            [category_count] => 1
            [category_description] => 
            [cat_name] => Транспорт
            [category_nicename] => transport
            [category_parent] => 0
        )

)

Now somehow get_categories term_id should be compared to my array and the objects rearranged accordingly.

TheDeadMedic · Accepted Answer · 2015-08-26 15:10:39Z

Long story short, build a new array with the categories indexed by ID. Then you can just loop over the date-sorted IDs and do with them as you wish:

$categories = get_categories();
$cats_index =
$cats_dates = array();

foreach( $categories as $category ) {
    // Index the categories by their ID
    $cats_index[ $category->term_id ] = $category;

    $posts = get_posts(
        array(
            'ignore_sticky_posts' => true,
            'posts_per_page' => 1,
            'category__in' => array( $category->term_id ),
        )
    );

    if ( $posts )
        $cats_dates[ $category->term_id ] = ( int ) mysql2date( 'U', $posts[0]->post_date_gmt );
    else
        $cats_dates[ $category->term_id ] = 0;
}

arsort( $cats_dates );

foreach ( array_keys( $cats_dates ) as $cat_id ) {
    // Loop over category IDs by date descending
    $category = $cats_index[ $cat_id ];
}

I did manage to do it with usort like pastebin.com/yCJNPVGv but it seems like your suggestion is a bit more tidy. — Georgi Demirev
– Georgi Demirev, Commented Aug 26, 2015 at 16:21

JHoffmann · Accepted Answer · 2015-08-26 12:34:29Z

0

usort uses a callback function to sort an array:

$categories_order = array_flip($categories_order);
$categories = usort( get_categories(), function( $a, $b ) {
    return $categories_order( $a['term_id'] ) - $categories_order( $b['term_id'] );
}

answered Aug 26, 2015 at 12:34

JHoffmann

1,88014 silver badges19 bronze badges

This doesn't seem to work. It's missing a closing bracket and semicolon. Even with that it returns PHP error "Fatal error: Function name must be a string in...". I had my eye on usort earlier, but even after reading on PHP docs I still can't seem to comprehend how the function actually works.

Georgi Demirev
– Georgi Demirev

2015-08-26 12:58:41 +00:00
Commented Aug 26, 2015 at 12:58

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