This is a modified version of thomas' range_string() function. It's simpler, cleaner, and more robust, but it lacks the advanced features his function had, hopefully it will be of assitance to someone.

Examples:

    input: "1, 2, 3, 4, 5, 6" --> output: 1, 2, 3, 4, 5, 6
    input: "1-6" --> output: 1, 2, 3, 4, 5, 6
    input: "1-6" --> output: 1, 2, 3, 4, 5, 6
    input: "1 - -6" --> output: 1, 2, 3, 4, 5, 6
    input: "0 - 0" --> output: 0
    input: "1, 4-6, 2" --> output: 1, 2, 4, 5, 6
    input: "6,3-1" --> output: 1, 2, 3, 6

<?php

define('RANGE_ARRAY_SORT', 1);
define('RANGE_ARRAY', 2);
define('RANGE_STRING_SORT', 3);
define('RANGE_STRING', 4);

function range_string($range_str, $output_type = RANGE_ARRAY_SORT)
{
    // Remove spaces and nother non-essential characters
    $find[]    = "/[^\d,\-]/";
    $replace[] = "";
    
    // Remove duplicate hyphens
    $find[]    = "/\-+/";
    $replace[] = "-";
    
    // Remove duplicate commas
    $find[]    = "/\,+/";
    $replace[] = ",";
    
    $range_str = preg_replace($find, $replace, $range_str);

    // Remove any commas or hypens from the end of the string
    $range_str = trim($range_str,",-");
    
    $range_out = array();
    $ranges    = explode(",", $range_str);
    
    foreach($ranges as $range)
    {
        
        if(is_numeric($range) || strlen($range) == 1)
        {
            // Just a number; add it to the list.
            $range_out[] = (int) $range;
        }
        else if(is_string($range))
        {
            
            // Is probably a range of values.
           $range_exp = preg_split("/(\D)/",$range,-1,PREG_SPLIT_DELIM_CAPTURE);
        
            $start = $range_exp[0];
            $end   = $range_exp[2];
        
            if($start > $end)
            {
                for($i = $start; $i >= $end; $i -= 1)
                {
                    $range_out[] = (int) $i;
                }
            }
            else
            {
                for($i = $start; $i <= $end; $i += 1)
                {
                    $range_out[] = (int) $i;
                }
            }
            
        }
    }
    
    switch ($output_type) {
        case RANGE_ARRAY_SORT:
            $range_out = array_unique($range_out);
            sort($range_out);
            
        case RANGE_ARRAY:
            return $range_out;
            break;
            
        case RANGE_STRING_SORT:
            $range_out = array_unique($range_out);
            sort($range_out);
            
        case RANGE_STRING:
        
        default:
            return implode(", ", $range_out);
            break;
    }
}

// Sample Usage:
$range = range_string("6, 3-1");

?>