WordPress - List all authors of a blog grouped by first name with a single letter as a header character.

gistfile1.aw

<?php

/** 
 *	List Users Alphabetically
 *
 *	Create a list of all authors of a WordPress blog.
 *	Names are grouped by first name with a single letter
 *	as a header character.
 *
 *      Call the function with <?php ngtj_list_users_alphabetically(); ?>
 *      where you want the list to appear.
 *
 *	@author		Nate Jacobs
 *	@link		https://gist.github.com/1321741
 */
function ngtj_list_users_alphabetically()
{
	$users = get_users( 'orderby=user_login&role=author' ); 

	$first_letter = '';
	foreach( $users as $user )
	{
		$space = strpos( $user->user_login, ' ' );
		$letter = substr( $user->user_login, 0, 1 );
		$letter = strtoupper( $letter );
		
		if ( $letter != $first_letter )
		{
			$first_letter = $letter;
		echo "<h4 id='ft_contrib_alphaletter_$first_letter'>$first_letter</h4>"; 
		}
		echo '<a href="' . get_author_posts_url( $user->ID, $user->user_nicename ) . '" title="' . $user->display_name . '">' . $user->display_name . '</a>';
		echo "<br>";
	}
}