You need to display current year and previous year in report.
In such case,You have an attribute named year,that should be placed in Report grid.
And year prompt created with Year attribute which has number of years.
Create a new report with placing year prompt into Report filter,and keep year attribute into report grid.
For getting previous year for year selected from Year prompt dynamically,you should create new transformation for year attribute.
By default you are having Previous year or else give calculation like,(Year-1).