Need to filter your Custom Post Types (WordPress) by Author in WPAdmin? Here's a handy way to do it by adding a new drop down for filtering

Filter Custom Posts by Author in WP-ADmin.php

<?php
add_action( 'restrict_manage_posts', 'admin_posts_filter_restrict_manage_posts_by_author' );
/**
 * Create the drop down
 *
 * @return void
 */
function admin_posts_filter_restrict_manage_posts_by_author(){
	if (isset($_GET['post_type']) && 'task' == $_GET['post_type']){
		wp_dropdown_users( array(
			'show_option_all' => __( 'Show All Authors', 'your-site' ),
			'name' => 'bcust_id',
			'selected' => $_GET['bcust_id']
		));
	}
}

add_filter( 'parse_query', 'modify_query_to_filter_by_author' );
/**
 * Filter by author
 * @param  (wp_query object) $query
 *
 * @return Void
 */
function modify_query_to_filter_by_author( $query ){
	global $pagenow;
	if ( isset($_GET['post_type']) 
	     && 'task' == $_GET['post_type'] 
	     && is_admin() && 
	     $pagenow == 'edit.php' 
	     && isset($_GET['bcust_id']) 
	     && $_GET['bcust_id'] != '') {
		$query->query_vars['author'] = $_GET['bcust_id'];
	}
}