$arr=array (
'1' => array ( 'date' => '2011-08-18', 'num' => 5 ) ,
'2' => array ( 'date' => '2011-08-20', 'num' => 3 ) ,
'3' => array ( 'date' => '2011-08-17', 'num' => 10 )
 )  ;


 $result = sysSortArray($arr,'num');

$arr=array (
'1' => array ( 'date' => '2011-08-18', 'num' => 3 ) ,
'2' => array ( 'date' => '2011-08-20', 'num' => 5 ) ,
'3' => array ( 'date' => '2011-08-17', 'num' => 10 )
 )  ;

/**
 * @package     二维数组排序
 * @version     $Id: FunctionsMain.inc.php,v 1.32 2011/09/24 11:38:37 wwccss Exp $
 *
 *
 * Sort an two-dimension array by some level two items use array_multisort() function.
 *
 * sysSortArray($Array,"Key1","SORT_ASC","SORT_RETULAR","Key2";……)
 * @author                      lamp100
 * @param  array   $ArrayData   the array to sort.
 * @param  string  $KeyName1    the first item to sort by.
 * @param  string  $SortOrder1  the order to sort by("SORT_ASC"|"SORT_DESC")
 * @param  string  $SortType1   the sort type("SORT_REGULAR"|"SORT_NUMERIC"|"SORT_STRING")
 * @return array                sorted array.
 */
function sysSortArray($ArrayData,$KeyName1,$SortOrder1 = "SORT_ASC",$SortType1 = "SORT_REGULAR")
{
    if(!is_array($ArrayData))
    {
        return $ArrayData;
    }

    // Get args number.
    $ArgCount = func_num_args();

    // Get keys to sort by and put them to SortRule array.
    for($I = 1;$I < $ArgCount;$I ++)
    {
        $Arg = func_get_arg($I);
        if(!eregi("SORT",$Arg))
        {
            $KeyNameList[] = $Arg;
            $SortRule[]    = '$'.$Arg;
        }
        else
        {
            $SortRule[]    = $Arg;
        }
    }

    // Get the values according to the keys and put them to array.
    foreach($ArrayData AS $Key => $Info)
    {
        foreach($KeyNameList AS $KeyName)
        {
            ${$KeyName}[$Key] = $Info[$KeyName];
        }
    }

    // Create the eval string and eval it.
    $EvalString = 'array_multisort('.join(",",$SortRule).',$ArrayData);';
    eval ($EvalString);
    return $ArrayData;
}