Custom product loop avoiding duplicates

Question

I am trying to create a product loop based on an attribute value from (pa_product-series). many products can have the same value, but I only want to return one from each...avoiding multiple products with same value.

Example (xxxx is the product-series):

product 1 - x400
product 2 - x400
product 3 - x500
product 4 - x600
product 5 - x600

Results should only show product 1, product 3 and product 4.

This is the code I have so far, but its returning an empty array

global $product;

$prod_series = $product->get_attribute( 'pa_product-series' );

$postid = get_the_ID();

$args = array(
    'post_type' => 'product',
    'orderby' => 'title',
    'order' => 'asc',
    'posts_per_page' => 10,
    'tax_query' => array(
    'relation' => '', array(
            'taxonomy' => 'pa_product-series',
            'field'      => 'slug',
            'terms'    => $prod_series
        ),
  )
);

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


        foreach( wc_get_product_terms($loop->post->ID, 'pa_product-series' ) as $attribute_value ):
            $term_names[$attribute_value] = $attribute_value;
        endforeach;
    endwhile;

    print_r($attribute_value);

else:
   echo '<span>No SKUs matches found</span>';
endif;

wp_reset_postdata();

when I use print_r($attribute_value), it returns the following:

WP_Term Object ( 
[term_id] => 1687 
[name] => CT0201CSF 
[slug] => ct0201csf 
[term_group] => 0 
[term_taxonomy_id] => 1687 
[taxonomy] => pa_product-series 
[description] => 
[parent] => 0 
[count] => 2 
[filter] => raw 
[term_order] => 0 
)
WP_Term Object ( 
[term_id] => 1687 
[name] => CT0201CSF 
[slug] => ct0201csf 
[term_group] => 0 
[term_taxonomy_id] => 1687 
[taxonomy] => pa_product-series 
[description] => 
[parent] => 0 
[count] => 2 
[filter] => raw 
[term_order] => 0 
)

I need to limit to 1 result per term_id or name...

Answer 1

Using the developers' reference example, you are referencing $loop redundantly. Drop the $loop-> before the_post() and have_posts():

if ( have_posts() ) {
    $term_names = array();
    while ( have_posts() ) {

        the_post(); 
        $myPostID = get_the_ID();

        //Uncomment next 3 lines to debug using your error log
        //ob_start();
        //var_dump($myPostID);
        //error_log('myPostID = ' . ob_get_clean(),0);

        $arrProductTerms = wc_get_product_terms( $myPostID, 'pa_product-series' );

        //Uncomment next 3 lines to debug using your error log
        //ob_start();
        //var_dump($arrProductTerms);
        //error_log('arrProductTerms = ' . ob_get_clean(),0);

        foreach($arrProductTerms as $att){
           // prevent later values from overwriting existing...
           // Also, I believe $att is an object with properties, so you need to choose which one should be unique. I chose "slug"
           if (!array_key_exists($att->slug,$term_names)) $term_names[$att->slug]=$att;
        } // loop foreach

    } // loop while
    // sort by key ($att->slug)
    ksort($term_names);

    // Used array_keys because we stored $att as objects
    echo '<span>' . implode( '</span>, <span>', array_keys($term_names) ) . '</span> ';

} else {
    echo '<span>No SKUs matches found</span>';
}  // end if

If that doesn't get it, I would use the error_log() call to closely examine the output of wc_get_product_terms() to see if you are getting what you expect.