public function filterByFunc($cb)
    {
        //method filters the collection using the given callback, keeping only those rows that pass a given truth test
        $dstore = new DataStore;
        $dstore->meta($this->metaData);
        foreach ($this->rows as $index=>$row) {
            if ($cb($row, $index)===true) {
                $dstore->append($row);
            }
        }
        return $dstore;
    }