<?php

function array_sort_by_fields(&$data, $sortby){
      static $sort_funcs = array();
     
    if (empty($sort_funcs[$sortby]))
    {
        $code = "\$c=0;";
        foreach (explode(',', $sortby) as $key)
        {
           $d = '1';
              if (substr($key, 0, 1) == '-')
              {
                 $d = '-1';
                 $key = substr($key, 1);
              }
              if (substr($key, 0, 1) == '#')
              {
                 $key = substr($key, 1);
               $code .= "if ( ( \$c = (\$a['$key'] - \$b['$key'])) != 0 ) return $d * \$c;\n";
              }
              else
              {
               $code .= "if ( (\$c = strcasecmp(\$a['$key'],\$b['$key'])) != 0 ) return $d * \$c;\n";
            }
        }
        $code .= 'return $c;';
        $sort_func = $sort_funcs[$sortby] = create_function('$a, $b', $code);
    }
    else
    {
        $sort_func = $sort_funcs[$sortby];
    }   
    uasort($data, $sort_func);   
}

#
# Modifier: sortby - allows arrays of named arrays to be sorted by a given field
#
function smarty_modifier_sortby($arrData,$sortfields) {
   array_sort_by_fields($arrData,$sortfields);
   return $arrData;
}

?>

http://www.smarty.net/forums/viewtopic.php?t=1079&sid=044cd556ed67f6ee4ed47e7cdeccd3ca

How to sort array in smarty template?

>> Create sort modifier file and save it in smarty / plugins with
modifier.sortby.php name 
use this modifier in smarty template like...
{foreach item=item key=key from=$users|@sortby:"firstname"}
{$item.id}-{$item.firstname}
{/foreach}

sort smarty array

sort, array

Smarty