Hi... I am trying to create a custom column that states what a value is as a % of a category field. Let me try and explain the problem in writing

I have costs broken down by department, cost code, product code i.e they are column headings and then a cost for each line

I know I can calculate for each row (cost) what that is as a percentage of the grand total.

What I would like to do is calculate what each value is as a % various fields 

i.e show me what the cost is as a percentage of all the costs against the code code recorded for that line? 

I assumed it would be a process when I

1- create a calculated column that sums all costs for the cost code. It's a subtotal but with a filter I guess.

2- create another column that divides the value for that row by that new column. This I know how to do.

Does that make sense in writing or should I go away and mock it up?