Snake case in WP

str_snake.php

<?php
/**
 * Convert a regular string to snake_case
 * For example, Hello World => hello_world
 * 
 * @param String $str String to be converted
 * @return String String in snake_case
 **/
function str_snake( $str )
{
    return str_replace( '-', '_', sanitize_title( $str ) );
}