Generate Letter Anchors for your Custom Post Types in WordPress

CPT-Letter-Anchors.php

<?php
$alphabet = range('A','Z');
$letters = array();
while( $the_query->have_posts() ) : $the_query->the_post();
	$lname = get_post_meta(get_the_ID(), $prefix.'lname', true);
	$first = strtoupper(substr(trim($lname), 0, 1));
	if($first && !in_array($first, $letters)){
		$letters[] = $first;
	}
endwhile;

echo '<ul class="letters">';
	foreach($alphabet as $letter){
		if(in_array($letter, $letters)){
			$format = '<li><a href="#%1$s">%1$s</a></li>';
		} else {
			$format = '<li><span>%1$s</span></li>';
		}
		
		echo sprintf($format, $letter);
	}
echo '</ul>';
?>