PL/SQL :: Analytical Functions In Group By

I have simplified this for ease of understanding. I have a Data column and a Month_ID column like this:

Values Month_ID
--------- -------------------------------------------------------
AAA 1
BBB 2

I split this out to values per year like this

Value_2011 Value_2012 Month_ID
-------------------------------------------------------------------------
AAA 1
BBB 2

Now i am trying to get the max(Value_2011) keep (dense_rank Last order by Month_ID) but i get a NULL. I can understand its because the Month_ID accomodates all years but i only need it to look at Month_ID for 2011 and return me the last dense_rank value, how can i achieve this?

I tried a couple of different methods like Last_Value() but i have group by in my original statement and i think analytical functions dont like GROUP by if they are not part of it. How can i achieve this?