How to automatically insert a list of related articles between the content

There are many ways to show related articles, such as code generated related posts with tumbnails. Here, I will show you another way. It is automatically insert a list of related articles between the content

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Insert the code below into the file functions.php :

// Code count the number of lines in text

function count_paragraph( $insertion, $paragraph_id, $content ) {

        $closing_p = '</p>';

        $paragraphs = explode( $closing_p, $content );

        foreach ($paragraphs as $index => $paragraph) {

                if ( trim( $paragraph ) ) {

                        $paragraphs[$index] .= $closing_p;

                }

                if ( $paragraph_id == $index + 1 ) {

                        $paragraphs[$index] .= $insertion;

                }

        }

        return implode( '', $paragraphs );

}

//Insert a list of related articles between the content

add_filter( 'the_content', 'prefix_insert_post_ads' );

function prefix_insert_post_ads( $content ) {

        $related_posts= do_shortcode('[related_posts_by_tax title=""]');

        if ( is_single() ) {

                return count_paragraph( $related_posts, 1, $content );

        }

        return $content;

}