How to do a 12-month average computation loop

So I have this data right here which spans from 2010 to 2014. I am trying to obtain the average of a 12month span.

For example, I am trying to obtain the 3rd column's average from Jan 2010~Dec 2010, then put the average on a row of a new matrix.

Next, I want to obtain the 3rd column's average from Feb 2010~Jan 2011, and put it on the new matrix's second row... and on.

Does anybody have an idea how to do this loop? I have a portion of my code but it is close to nil.

2039  40297.9168600000  2.60000000000000  2010  4
2009  40298.4671200000  1.40000000000000  2010  4
2151  40300.5642100000  0.900000000000000  2010  5
2144  40300.8513400000  2                  2010  5
2135  40302.3340300000  1.20000000000000  2010  5