Multiple Loop through Category Terms

multi-loop.php

<?php
function db_multi_term_custom_loop($atts, $content = null) {
    // Get all the categories
    $categories = get_terms( 'category' );

    ob_start();
    // Loop through the $category terms
    foreach ( $categories as $category ):
        // new query for each category term.
        $customQuery = new WP_Query(
            array(
                'post_type' => 'post',
                'showposts' => -1,
                'tax_query' => array(
                    array(
                        'taxonomy'  => 'category',
                        'terms'     => array( $category->slug ),
                        'field'     => 'slug'
                    )
                )
            )
        );
        // output category title and posts 
        ?>
        <h2><?php echo $category->name; ?></h2>
        <div class="gb-grid-wrapper gb-grid-wrapper-global">
        <?php while ($customQuery->have_posts()) : $customQuery->the_post(); ?>
            <div class="gb-grid-column gb-grid-column-global-33">
            <?php do_action('db_custom_post_loop'); ?>
            </div>
        <?php endwhile; ?>
        </div>

        <?php
        // Reset query
        $customQuery = null;
        wp_reset_postdata();

    // end the loop
    endforeach;
    return ob_get_clean();
}

add_shortcode('db_multi_term_loop', 'db_multi_term_custom_loop');