Calculate the value of a field "b" in GetFormatter function of a field "a"

Hi Allan. I use datatables 1.9.4
In the get.php I use a getFormatter function to calculate the value of a field

Field::inst( 'etl_product_desc' )->getFormatter( function($val, $data, $field) {
..... here I make a select and return the value of 'etl_product_desc' ...
}

Well, I need to calculate inside this function the value of another field that I retrive in this get.php with another "Field::inst"

Is possible ? How can I do ?

Thanks