I am trying to calculate monthly means by year of phosphates and nitrates from a multi year data set. Can anybody help me out with the most effective way to do this?

My data looks like this:

Collection_Date                   Test.Name              Value
2000-01-24 17:00:00            Phosphate               0.108
2000-01-24 17:00:00            Nitrate                     0.037
2001-11-12 08:45:00            Phosphate               0.45
...


Thanks and sorry for the blatantly "newbie" question.




      
	[[alternative HTML version deleted]]

