Powerpivot adding calculated item to a field - powerpivot

Question

I have data in a table stored in an Excel file. I linked this table into a PowerPivot Data Model, and from that Data Model I want to create a Pivot in the same Excel file. In this table one column contains split of data into: Budget, Last Year, Prior Forecast, Current Forecast. I want to add this field as Pivot coulmns, but I would like to add additional calc item (like in normal Excel Pivot Table I can add Calculated Item) with calculation: [Current Forecast] - [Prior Forecast]. I checked various pages, forums, etc. and I have not found any guidance on how to add such a calc item to a field in PowerPivot.
My input looks like this:
Sample data:
Category Client Amount
Current Forecast XYZ 600
Current Forecast ABC 1000
Current Forecast DEF 100
Prior Forecast XYZ 500
Prior Forecast ABC 1200
Budget XYZ 800
Budget ABC 900
Budget DEF 100
Last Year XYZ 700
Last Year ABC 500
From this data I want to create a Pivot that would look like this:
Current Prior Last
Client Forecast Forecast Budget Year FoF YoY
XYZ 600 500 800 700 100 -100
ABC 1000 1200 900 500 -200 500
DEF 100 100 100 100
In PowerPivot, I want to add two additional columns, perhaps as calculated items in the Category field:
FoF=[Current Forecast]-[Prior Forecast]
YoY=[Current Forecast]-[Last Year]
On below screenshots it is better visible, what I want to achieve:
I can't add this to my source data as the number of rows between current forecast and prior forecast are not in the same amount and not in the same order (they are extracted from another system)

Answer 1

Guenh, this should be quite straightforward:
Depending on your PowerPivot versions, you either create a new measure from PowerPivot ribbon (Excel 2010 Add-in: New Measure button). In Excel 2013, it was renamed to Calculated Field, still available via PowerPivot ribbon:
Anyway, I downloaded your data and created new measures (= calculated fields) for all of your columns, which was the key. The way your data is structured is not ideal, but it's certainly doable. First you have to sum the amount for each category, so use this simple CALCULATE formula:
-CALCULATE(SUM([Amount]),Table1[Category]="Budget")
What it does is that it sums the amount values, but only for rows have Budget in the Category column. The example above is defined for the Budget category; include the other three categories as well (simply duplicate the formula and change the second parameter in CALCULATE: instead of "Budget", use "Last Year", etc.
Then create your FoF and YoY calculations by simply using already created measures:
If you then add new PivotTable (from PowerPivot window), simply drag Client Name to rows section and all the measures to Values section.
With that, you should get your desired result table as shows below. Here you can download the source file (for Excel 2013).
Hope this helps :)

Answer 2

How to do realize calculated item in PowerPivot, usually it has many columns as KPI need to compare, amount, quantity, COST ect. as below 2. secondly most times the data that you want to put in comparison has to lie in row. Really ache to seek a solution, but seems Dax or PowerPivot has lost the function of calculated item.