On taxonomy page. Wanted to sort posts by their membership to a taxonomy. Loops through and re-orders as per the order of $terms array.

resort-posts-array.php

    /*
     * Used on taxonomy.php template by calling $posts = resort_posts($posts); 
     * =============================
     * Expects the $posts variable to be passed to it, and will loop through,
     * and move all the image gallery posts to the end of the loop.
     * 
     * Order is by following taxonomies:
     * - Media Releases
     * - Fact Sheets 
     * - Images
     * - Videos
     * - Audio Files
     * - Good News Stories  
     */
    function resort_posts( $posts=array() )
    {
        $new_posts = array();
        $terms = array( 'media-releases', 'fact-sheets', 'image-gallery', 'video-gallery', 'audio-files' );

        // Loop through each post. Then foreach post;
        // start checking what format it is & update the array.
        foreach( $posts as $key=>$post ){
            foreach( $terms as $term_key => $term ){
                if( has_term( $term, 'mc-format', $post ) ){
                    $new_array [ $term_key ][] = $post; 
                    unset($posts[$key]);
                    continue;
                }
            }
        }
        // Sort the keys, correct order
        ksort( $new_array );

        // Loop through and make a single level array now.
        foreach($new_array as $post_array)
            foreach($post_array as $post)
                $new_posts[] = $post;
        
        // $posts will contain any posts with no format, add them on last.
        $posts = array_merge( $new_posts, $posts );
        
        return $posts;
    }