Wordpress posts ordering by alphabetical for each letter

<?php 
	$posts = get_posts(
	    array(
	        'post_type' => 'post',
	        'post_status' => 'publish',
	        'posts_per_page' => -1,
	        'orderby' => 'title',
	        'order' => 'ASC',
	    )
	);
	$alphas = range('A', 'Z');
	$letter_keyed_posts = array();
	if ( $posts ) {
	    foreach ( $posts as $post ) {
	        $first_letter = strtoupper( substr( $post->post_title, 0, 1 ) );

	        if ( ! array_key_exists( $first_letter, $letter_keyed_posts ) ) {
	        	
	            $letter_keyed_posts[ $first_letter ] = array();
	        }

	         $letter_keyed_posts[ $first_letter ][] = $post;
	    }
	    
	}
	foreach ($letter_keyed_posts as $key => $value) {
		?>
		<table class="table">
		  <caption><h1 class="text-left">List of --> <?php echo $key; ?></h1></caption>
		  <thead>
		    <tr>
		      <th scope="col">#</th>
		      <th scope="col">Title</th>
		    </tr>
		  </thead>
		  <tbody>
			<?php foreach ($value as $val) {
		      	?>
				<tr>
				  <th scope="row"><?php echo $val->ID; ?></th>
				  <td><a href="<?php echo get_permalink( $val->ID ); ?>"><?php echo $val->post_title; ?></a></td>
				</tr>
		      	<?php
		    } ?>
		  </tbody>
		</table>
		<?php
	}
	?>