title: NumPY: Undestand how to sum every n values in an array matrix
body: <p>Hi folks,</p>
  
  <pre><code> array([[  3.,  12.,  21.,  30.],
             [  3.,  12.,  21.,  30.],
             [  3.,  12.,  21.,  30.],
             [  3.,  12.,  21.,  30.],
              ...
             [  3.,  12.,  21.,  30.]
             [  3.,  12.,  21.,  30.],
             [  3.,  12.,  21.,  30.],
             [  3.,  12.,  21.,  30.]])
  </code></pre>
  
  <p>How to sum every 29 rows in the same column:
  (3+3+3+3...) 29times. 
  Could be great to reshape the size of our array (1392, 8760) in a (48, 8760) after the sum of these values.
  I tried to look at the reshape and sum function but I am having a hard time to deeply understand how it works.</p>