prevent display duplicate titles on main page

Question

I am using a automatic rss post reader on my website and there is a problem with this plugin that sometimes publish duplicate posts.I can't do anything to this plugin but at least it is better if I could prevent to display the same titles on main page. here is my code

 <ul>
<?php  
                    $portfolio = new WP_Query(array(
                    'post_status' =>'publish',
                    'post_type' =>'post',
                    'cat' =>''.$link1.'',
                    'posts_per_page' =>'9'      
                    ));
 if($portfolio->have_posts()) : 
                    while($portfolio->have_posts()) : $portfolio->the_post();
                                    ?>
<li>
<a href="<?php the_permalink() ?>" target="_blank"><?php the_title(); ?></a>
</li>
<?php endwhile; endif; wp_reset_query(); ?>
</ul>

Answer 1

Your code should look like this to exclude duplicate titles

<ul>
    <?php
    // Initial counter for displayed posts.
    $counter = 1;
    // Initial empty array of displayed titles.
    $titles = [];

    $portfolio = new WP_Query([
        'post_status' => 'publish',
        'post_type' => 'post',
        'cat' => '' . $link1 . '',
        // Because we don't know the number of duplicate titles, fetch all.
        'posts_per_page' => -1,
    ]);

    if ( $portfolio->have_posts() ) :

        // Start the loop.
        while ( $portfolio->have_posts() ) : $portfolio->the_post();

            // If the current title has not been displayed already, display it.
            if ( ! in_array( get_the_title(), $titles ) ) {
                ?>
                <li>
                    <a href="<?php the_permalink(); ?>" target="_blank">
                        <?php the_title(); ?>
                    </a>
                </li>
                <?php
                // Mark current title as displayed by adding it to the titles array.
                $titles[] = get_the_title();
                // Increase counter.
                $counter++;

            }

            // When we have displayed 10 posts the loop should stop.
            if ( $counter == 10 ) {
                break;
            }

        endwhile; endif;
    wp_reset_query(); ?>
</ul>

I hope this may help!

Answer 2

You somehow have to get hold of the post IDs you want to exclude. By calling the plugin's WP_Query again for example and at best let you return only post IDs by 'fields' => 'ids' this time.

Then you can use the result to exclude these posts from your other queries by passing an array of post IDs to 'post__not_in'. So let's assume you created an array of the posts you want to exclude that looks like that $exlcude = [ 123, 456, 789 ] then the query needs to look like this:

$args = array(
    'post_status' =>'publish',
    'post_type' =>'post',
    'cat' => $link1,
    'posts_per_page' => '9',      
);

if ( ! empty( $exclude ) ) {
    $args['post__not_in'] = $exclude;
}

new WP_Query($args);