List terms of custom taxonomy if matches other taxonomy

Question

So the title is confusing but I can't think of a better way to word it. Basically, I have two taxonomies of "state" and "city" (that have to stay separate for other reasons). Lets say for instance, a term in the taxonomy of "state" is "Connecticut" I then want to display a list of terms from the taxonomy of "city" that populate only from posts with the "state" term as "Connecticut". Basically, I want to dynamically call the state and display the cities in the sidebar on the archive page... I know, this sounds really confusing.

This code works but obviously causes duplicates, I would like each one only listed once.

<?php
$pterms = get_the_terms( $post->ID, 'property_location' );

if ( $pterms && ! is_wp_error( $pterms ) ) : 

$prop_links = array();

foreach ( $pterms as $el_term ) {
    $prop_links[] = $el_term->name;
}

$st_location = join( ", ", $prop_links );   
?>
<?php endif; ?>
<?php endwhile; ?>

<!-- this is a separate loop -->

<?php
$args = array(
 'post_type' => 'property',
 'post_status' => 'publish',
 'posts_per_page' => -1,
 'property_location' => ''.$st_location.''
);
$the_query = new WP_Query( $args ); ?>
<?php while ($the_query->have_posts()) : $the_query->the_post(); ?>

<p><?php echo get_the_term_list( $post->ID, 'city', '', '', '' ); ?></p> 

<?php endwhile; ?>

Any suggestions?

Answer 1

Your approach isn't bad, but instead of echoing all of these out, you should store them in an array, then use array_unique to remove duplicate entries before displaying.

<?php 
$array_out = array();
while ($the_query->have_posts()) : $the_query->the_post(); ?>
    $terms = get_the_terms( $post->ID, 'city'); 
    foreach($terms as $term){
        $term_link = get_term_link($term, 'city');
        $array_out[] = '<a href="'.$term_link.'">'.$term->name.'</a>';
    }
endwhile; 

$array_clean = array_unique($array_out);
echo '<p>' . implode('</p><p>', $array_clean) . '</p>';

We have to build the link ourselves using get_term_link() so the array holds each term separately, not by group as it is related to each post.