Wordpress loop showing duplicate categories

Question

I'm trying to create a loop that displays a list of the categories (as buttons) of a custom post type. I have a loop that works, but it is looping through all the custom posts and display each category. So right now if I have two posts with the same category, it will display that same category twice. Also I need to echo out custom classes for my isotope filter to work.

This is my code:

            <?php
            $args = array( 
                'post_type' => 'ondernemers', 
                'posts_per_page' => 10
                 );

            $loop = new WP_Query( $args );
            while ( $loop->have_posts() ) : $loop->the_post();

            $categories = get_the_category( $post->ID, 'taxonomy' );
            foreach( $categories as $category ) {
                echo '<button class="button" data-filter=".'  . $category->slug . ' "><div class="button-img-' . $category->slug . '"></div>' . $category->name . '</button>';
            }

            endwhile;
            ?>

Is there a way to make the loop print each category only once, instead of once for each time it is just for each unique post?

Answer 1

Use below code to retrieve category name of a custom post type.

<?php 
    $args = array(
        'type'                     => 'post', /* custom post type name */
        'parent'                   => '',
        'orderby'                  => 'id',
        'order'                    => 'ASC',
        'hide_empty'               => 1,
        'hierarchical'             => 1,   
        'taxonomy'                 => 'category'  /* custom post type texonomy name */
    ); 
    $cats = get_categories($args);
    foreach ($cats as $cat) {           
        $cat_id= $cat->term_id;
        $cat_name= $cat->name; ?>
        <h3><?php echo '<a href="' . get_category_link( $cat_id ) . '">'.$cat->name.'</a>'; ?></h3>      
    <?php  } ?>