jQuery.fn.dataTableExt.aTypes.push(  
    function ( sData )  
    {  
        var sValidChars = "0123456789.-,";  
        var Char;  
          
        /* Check the numeric part */  
        for ( i=1 ; i<sData.length ; i++ )   
        {   
            Char = sData.charAt(i);   
            if (sValidChars.indexOf(Char) == -1)   
            {  
                return null;  
            }  
        }  
          
        /* Check prefixed by currency */  
        if ( sData.charAt(0) == '$' || sData.charAt(0) == '£' )  
        {  
            return 'currency';  
        }  
        return null;  
    }  
);