Converting months into Quarters.

Create Quarters from Date

There are probably many ways to do this, but I would use the built in date
functions such as:

extract(month,[date]) which will give you the numeric month.
then do a case statement such as: 

case extract(month,[date])
when 1 then 1^st  
when 2 then 1^st  
when 3 then 1^st  
when 4 then 2^nd

When 5 then 2^nd

When 6 then 2^nd

When 7 then 3^rd  

When 8 then 3^rd  

When 9 then 3^rd  

When 10 then 4^th

When 11 then 4^th  

When 12 then 4^th

end 

Now you will have a dataitem which contains the quarter.
You can use it as you desire.