是的，你离它很近。只需使用$postarr 此过滤器的参数：

add_filter( \'wp_insert_post_data\' , \'wpse128138_wp_insert_post_data\', 99, 2 );
function wpse128138_wp_insert_post_data( $data, $postarr ) {

    // run this only for posts
    if ( \'post\' != $postarr[\'post_type\'] )
        return $data;

    foreach( $postarr[\'post_category\'] as $category_id ) {
        if ( is_wp_error( $category = get_category( $category_id ) ) )
            continue; // invalid category, just pass

        // and here you can safely use the $category object
    }

    return $data;
}