Get and separate posts by months

get-posts-by-month.php

<?php
/**
 * @author https://wordpress.stackexchange.com/users/10097/david-gard
 * @link https://wordpress.stackexchange.com/questions/176141/display-posts-by-month
 */

$time_start = microtime(true);

/** Set up a date interval object for 6 monts ago (you can change as required) */
$interval = new DateInterval('P6M');
$interval->invert = 1;

/** Grab the date as it was 6 months ago */
$date = new DateTime(date('Y-m-d'));
$date->add($interval);

/** Query the database for all posts newer than the the given date interval */
$args = array(
    'nopaging'          => true,
    'posts_per_page'    => -1,
    'post_type'         => 'post',
    'post_status'       => 'publish',
    'orderby'           => 'date',
    'date_query'        => array(
        'after' => $date->format('Y-m-d')
    )
);
$month_query = new WP_Query($args);

/** Check to ensure that there are articles for this month... */
if($month_query->have_posts()) :

    $month_titles = array();
    $close_ul = false;
    
    /** Set the attributes for displaying the title as an attribute */
    $title_attribute_args = array(
        'before'    => 'Visit article \'',
        'after'     => '\' ',
        'echo'      => false
    );      
    
    /** Loop through each post for this month... */
    while($month_query->have_posts()) : $month_query->the_post();
    
        /** Check the month/year of the current post */
        $month_title = date('F Y', strtotime(get_the_date('Y-m-d H:i:s')));
        
        /** Maybe output a human friendly date, if it's not already been output */
        if(!in_array($month_title, $month_titles)) :
        
            if($close_ul) echo '</ul>';                                                             // Check if the unordered list of posts should be closed (it shouldn't for the first '$monthe_title')
            echo '<h1 style="padding-left: 250px;" id="monthly-title">' . $month_title . '</h1>';   // Output the '$month_title'
            echo '<ul style="padding-left: 250px;" id="monthly-posts">';                            // Open an unordered lists for the posts that are to come
            $month_titles[] = $month_title;                                                         // Add this `$month_title' to the array of `$month_titles` so that it is not repeated
            $close_ul = true;                                                                       // Indicate that the unordered list should be closed at the next oppurtunity
            
        endif;
        
        /** Output each article for this month */
        printf(
            '<li id="monthly-post-%1$s">%2$s <a href="%3$s" title="%4$s">%3$s</a></li>',
            get_the_ID(),                               /** %1$s - The ID of the post */
            get_the_title(),                            /** %2$s - The article title */
            get_permalink(get_the_ID()),                /** %3$s - The article link */
            the_title_attribute($title_attribute_args)  /** %4$s - The title for use as an attribute */
        );
        
    endwhile;
    
    if($close_ul) echo '</ul>'; // Close the last unordered list of posts (if there are any shown)
    
endif;

/** Reset the query so that WP doesn't do funky stuff */
wp_reset_query();