Did you ever saw or designed a way to switch column content through its column header? I've done this before for units or switching between numbers and percentage, but this time its a less obvious switching...
In the below example I used a dropdown so the user can select to see his spendings as '% of total budget' or as '% of the Leisure and Culture budget'.
Is a dropdown (with single selection) is the way to go? or would you use a more prominent control above the table (I have a fairly limited space in the real life design)?